diff --git a/2023/day24/solution.c b/2023/day24/solution.c
index 2fe49ee..f648933 100644
--- a/2023/day24/solution.c
+++ b/2023/day24/solution.c
@@ -3,6 +3,8 @@
 #include "parse.h"
 #include "printf.h"
 
+#include "double.h"
+
 struct vec3 {
   double x;
   double y;
@@ -48,14 +50,6 @@ static bool line_line_intersection_2d(vec3 * a, vec3 * da,
   return true;
 }
 
-static double int64_to_double(int64_t n)
-{
-  double l = (uint32_t)n;
-  double h = (int32_t)(n >> 32);
-
-  return h * 4294967296.0 + l;
-}
-
 static const char * parse_line(const char * input, vec3 * p, vec3 * v)
 {
   int64_t x, y, z;
@@ -81,12 +75,12 @@ static const char * parse_line(const char * input, vec3 * p, vec3 * v)
   input = parse_skip(input, ' ');
   input = parse_skip(input, '\n');
 
-  p->x = int64_to_double(x);
-  p->y = int64_to_double(y);
-  p->z = int64_to_double(z);
-  v->x = int64_to_double(dx);
-  v->y = int64_to_double(dy);
-  v->z = int64_to_double(dz);
+  p->x = (double)(x);
+  p->y = (double)(y);
+  p->z = (double)(z);
+  v->x = (double)(dx);
+  v->y = (double)(dy);
+  v->z = (double)(dz);
 
   return input;
 }
diff --git a/2024/day13/input.txt b/2024/day13/input.txt
new file mode 100644
index 0000000..3b53baf
--- /dev/null
+++ b/2024/day13/input.txt
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+Button B: X+75, Y+55
+Prize: X=9696, Y=14311
+
+Button A: X+41, Y+79
+Button B: X+58, Y+19
+Prize: X=4374, Y=5367
+
+Button A: X+47, Y+14
+Button B: X+35, Y+66
+Prize: X=17301, Y=1534
+
+Button A: X+68, Y+29
+Button B: X+21, Y+98
+Prize: X=6996, Y=5833
+
+Button A: X+16, Y+61
+Button B: X+72, Y+15
+Prize: X=10896, Y=9927
+
+Button A: X+69, Y+16
+Button B: X+17, Y+99
+Prize: X=4411, Y=2924
+
+Button A: X+16, Y+73
+Button B: X+43, Y+42
+Prize: X=2463, Y=4299
+
+Button A: X+54, Y+16
+Button B: X+21, Y+43
+Prize: X=4187, Y=10273
+
+Button A: X+49, Y+13
+Button B: X+49, Y+83
+Prize: X=6076, Y=4902
+
+Button A: X+40, Y+19
+Button B: X+17, Y+31
+Prize: X=18121, Y=6893
+
+Button A: X+22, Y+89
+Button B: X+62, Y+33
+Prize: X=3470, Y=2929
+
+Button A: X+24, Y+51
+Button B: X+51, Y+11
+Prize: X=13013, Y=7760
+
+Button A: X+40, Y+72
+Button B: X+94, Y+29
+Prize: X=10730, Y=8799
+
+Button A: X+85, Y+18
+Button B: X+64, Y+86
+Prize: X=3858, Y=4222
+
+Button A: X+99, Y+11
+Button B: X+18, Y+71
+Prize: X=1530, Y=722
+
+Button A: X+69, Y+12
+Button B: X+93, Y+98
+Prize: X=11136, Y=9792
+
+Button A: X+95, Y+75
+Button B: X+21, Y+96
+Prize: X=917, Y=1677
+
+Button A: X+22, Y+57
+Button B: X+46, Y+17
+Prize: X=7332, Y=17866
+
+Button A: X+55, Y+19
+Button B: X+27, Y+67
+Prize: X=8606, Y=17118
+
+Button A: X+42, Y+92
+Button B: X+77, Y+50
+Prize: X=3416, Y=2736
+
+Button A: X+13, Y+64
+Button B: X+92, Y+86
+Prize: X=5175, Y=6030
+
+Button A: X+56, Y+18
+Button B: X+20, Y+46
+Prize: X=4068, Y=5212
+
+Button A: X+78, Y+11
+Button B: X+19, Y+79
+Prize: X=6081, Y=10602
+
+Button A: X+19, Y+87
+Button B: X+84, Y+35
+Prize: X=3342, Y=3765
+
+Button A: X+57, Y+33
+Button B: X+19, Y+43
+Prize: X=8062, Y=8686
+
+Button A: X+93, Y+60
+Button B: X+14, Y+72
+Prize: X=1229, Y=2556
+
+Button A: X+55, Y+24
+Button B: X+14, Y+94
+Prize: X=1871, Y=6002
+
+Button A: X+13, Y+19
+Button B: X+37, Y+15
+Prize: X=11560, Y=7340
+
+Button A: X+97, Y+92
+Button B: X+68, Y+14
+Prize: X=12918, Y=8566
+
+Button A: X+64, Y+16
+Button B: X+19, Y+58
+Prize: X=15227, Y=15866
+
+Button A: X+12, Y+62
+Button B: X+63, Y+17
+Prize: X=11813, Y=12953
+
+Button A: X+72, Y+28
+Button B: X+20, Y+52
+Prize: X=1284, Y=4264
+
+Button A: X+76, Y+17
+Button B: X+23, Y+38
+Prize: X=8199, Y=4101
+
+Button A: X+84, Y+38
+Button B: X+17, Y+47
+Prize: X=7592, Y=6422
+
+Button A: X+76, Y+26
+Button B: X+33, Y+61
+Prize: X=7100, Y=3622
+
+Button A: X+53, Y+45
+Button B: X+14, Y+48
+Prize: X=3495, Y=4737
+
+Button A: X+14, Y+57
+Button B: X+95, Y+13
+Prize: X=2193, Y=4817
+
+Button A: X+91, Y+24
+Button B: X+39, Y+44
+Prize: X=8905, Y=4776
+
+Button A: X+36, Y+95
+Button B: X+54, Y+14
+Prize: X=6570, Y=8985
+
+Button A: X+47, Y+26
+Button B: X+27, Y+45
+Prize: X=9856, Y=1870
+
+Button A: X+70, Y+23
+Button B: X+33, Y+80
+Prize: X=6705, Y=3932
+
+Button A: X+93, Y+22
+Button B: X+72, Y+97
+Prize: X=13317, Y=8748
+
+Button A: X+68, Y+56
+Button B: X+12, Y+82
+Prize: X=3792, Y=5070
+
+Button A: X+91, Y+19
+Button B: X+50, Y+58
+Prize: X=7149, Y=4917
+
+Button A: X+17, Y+85
+Button B: X+62, Y+56
+Prize: X=6472, Y=11278
+
+Button A: X+71, Y+18
+Button B: X+16, Y+75
+Prize: X=7574, Y=7170
+
+Button A: X+13, Y+78
+Button B: X+64, Y+76
+Prize: X=3350, Y=6856
+
+Button A: X+65, Y+14
+Button B: X+16, Y+42
+Prize: X=8942, Y=19674
+
+Button A: X+37, Y+19
+Button B: X+20, Y+33
+Prize: X=15445, Y=3074
+
+Button A: X+12, Y+40
+Button B: X+76, Y+26
+Prize: X=1848, Y=19728
+
+Button A: X+86, Y+16
+Button B: X+11, Y+96
+Prize: X=7116, Y=9216
+
+Button A: X+62, Y+14
+Button B: X+49, Y+69
+Prize: X=5138, Y=6722
+
+Button A: X+44, Y+63
+Button B: X+42, Y+17
+Prize: X=10920, Y=3470
+
+Button A: X+51, Y+26
+Button B: X+35, Y+55
+Prize: X=11198, Y=1063
+
+Button A: X+85, Y+11
+Button B: X+11, Y+72
+Prize: X=507, Y=16765
+
+Button A: X+50, Y+17
+Button B: X+28, Y+55
+Prize: X=2500, Y=4978
+
+Button A: X+17, Y+41
+Button B: X+60, Y+38
+Prize: X=11731, Y=5537
+
+Button A: X+31, Y+41
+Button B: X+91, Y+36
+Prize: X=9013, Y=6353
+
+Button A: X+62, Y+21
+Button B: X+15, Y+59
+Prize: X=1794, Y=13288
+
+Button A: X+41, Y+14
+Button B: X+26, Y+49
+Prize: X=7670, Y=3910
+
+Button A: X+24, Y+99
+Button B: X+95, Y+54
+Prize: X=8639, Y=10971
+
+Button A: X+13, Y+80
+Button B: X+93, Y+52
+Prize: X=4898, Y=7248
+
+Button A: X+97, Y+73
+Button B: X+31, Y+83
+Prize: X=6926, Y=10702
+
+Button A: X+21, Y+86
+Button B: X+90, Y+65
+Prize: X=7887, Y=8317
+
+Button A: X+37, Y+42
+Button B: X+83, Y+27
+Prize: X=7887, Y=3105
+
+Button A: X+19, Y+68
+Button B: X+67, Y+25
+Prize: X=3042, Y=7375
+
+Button A: X+30, Y+51
+Button B: X+80, Y+15
+Prize: X=2140, Y=2670
+
+Button A: X+87, Y+22
+Button B: X+49, Y+91
+Prize: X=6983, Y=3338
+
+Button A: X+74, Y+42
+Button B: X+14, Y+40
+Prize: X=8560, Y=1180
+
+Button A: X+98, Y+11
+Button B: X+53, Y+87
+Prize: X=4734, Y=3125
+
+Button A: X+36, Y+60
+Button B: X+94, Y+15
+Prize: X=6512, Y=2070
+
+Button A: X+36, Y+11
+Button B: X+33, Y+57
+Prize: X=15008, Y=16375
+
+Button A: X+79, Y+51
+Button B: X+18, Y+46
+Prize: X=12284, Y=18892
+
+Button A: X+25, Y+63
+Button B: X+66, Y+18
+Prize: X=12741, Y=16919
+
+Button A: X+11, Y+54
+Button B: X+76, Y+33
+Prize: X=4920, Y=6683
+
+Button A: X+23, Y+71
+Button B: X+55, Y+17
+Prize: X=15713, Y=18075
+
+Button A: X+92, Y+85
+Button B: X+72, Y+14
+Prize: X=11088, Y=6988
+
+Button A: X+90, Y+31
+Button B: X+15, Y+41
+Prize: X=8280, Y=5217
+
+Button A: X+16, Y+52
+Button B: X+72, Y+24
+Prize: X=15496, Y=13792
+
+Button A: X+17, Y+24
+Button B: X+76, Y+16
+Prize: X=8548, Y=3760
+
+Button A: X+21, Y+42
+Button B: X+56, Y+20
+Prize: X=3955, Y=3034
+
+Button A: X+57, Y+15
+Button B: X+16, Y+20
+Prize: X=3915, Y=1125
+
+Button A: X+64, Y+16
+Button B: X+25, Y+70
+Prize: X=12199, Y=10666
+
+Button A: X+13, Y+57
+Button B: X+36, Y+13
+Prize: X=12196, Y=1889
+
+Button A: X+50, Y+70
+Button B: X+29, Y+13
+Prize: X=19005, Y=11065
+
+Button A: X+58, Y+87
+Button B: X+76, Y+34
+Prize: X=6738, Y=7227
+
+Button A: X+79, Y+62
+Button B: X+24, Y+88
+Prize: X=2126, Y=1876
+
+Button A: X+29, Y+89
+Button B: X+70, Y+22
+Prize: X=7399, Y=4003
+
+Button A: X+61, Y+36
+Button B: X+12, Y+47
+Prize: X=7624, Y=15339
+
+Button A: X+16, Y+27
+Button B: X+43, Y+14
+Prize: X=15461, Y=6925
+
+Button A: X+53, Y+14
+Button B: X+17, Y+53
+Prize: X=1833, Y=2085
+
+Button A: X+12, Y+46
+Button B: X+76, Y+33
+Prize: X=17232, Y=7631
+
+Button A: X+23, Y+15
+Button B: X+11, Y+32
+Prize: X=2079, Y=2051
+
+Button A: X+14, Y+61
+Button B: X+79, Y+31
+Prize: X=19076, Y=19749
+
+Button A: X+67, Y+97
+Button B: X+95, Y+39
+Prize: X=12736, Y=11344
+
+Button A: X+14, Y+23
+Button B: X+35, Y+11
+Prize: X=6444, Y=17109
+
+Button A: X+14, Y+40
+Button B: X+32, Y+17
+Prize: X=5020, Y=6220
+
+Button A: X+53, Y+14
+Button B: X+14, Y+42
+Prize: X=17332, Y=3966
+
+Button A: X+43, Y+16
+Button B: X+12, Y+25
+Prize: X=2577, Y=12758
+
+Button A: X+26, Y+12
+Button B: X+24, Y+47
+Prize: X=17828, Y=3061
+
+Button A: X+99, Y+66
+Button B: X+43, Y+91
+Prize: X=6135, Y=8391
+
+Button A: X+13, Y+41
+Button B: X+63, Y+12
+Prize: X=6296, Y=12458
+
+Button A: X+18, Y+42
+Button B: X+88, Y+22
+Prize: X=2486, Y=1034
+
+Button A: X+35, Y+80
+Button B: X+52, Y+37
+Prize: X=5416, Y=8041
+
+Button A: X+81, Y+32
+Button B: X+21, Y+50
+Prize: X=3750, Y=1690
+
+Button A: X+90, Y+27
+Button B: X+17, Y+82
+Prize: X=3355, Y=6005
+
+Button A: X+35, Y+14
+Button B: X+35, Y+48
+Prize: X=13850, Y=6312
+
+Button A: X+94, Y+82
+Button B: X+14, Y+41
+Prize: X=4962, Y=6027
+
+Button A: X+18, Y+86
+Button B: X+36, Y+31
+Prize: X=2826, Y=8849
+
+Button A: X+24, Y+42
+Button B: X+57, Y+26
+Prize: X=4289, Y=16742
+
+Button A: X+15, Y+59
+Button B: X+76, Y+27
+Prize: X=12775, Y=18008
+
+Button A: X+64, Y+27
+Button B: X+20, Y+65
+Prize: X=19348, Y=11874
+
+Button A: X+27, Y+55
+Button B: X+85, Y+14
+Prize: X=2653, Y=1903
+
+Button A: X+90, Y+12
+Button B: X+47, Y+90
+Prize: X=681, Y=342
+
+Button A: X+13, Y+29
+Button B: X+18, Y+13
+Prize: X=2527, Y=8550
+
+Button A: X+71, Y+34
+Button B: X+25, Y+59
+Prize: X=10411, Y=6369
+
+Button A: X+78, Y+26
+Button B: X+61, Y+98
+Prize: X=7284, Y=3360
+
+Button A: X+49, Y+78
+Button B: X+47, Y+11
+Prize: X=8090, Y=8347
+
+Button A: X+65, Y+29
+Button B: X+23, Y+59
+Prize: X=3886, Y=2806
+
+Button A: X+13, Y+58
+Button B: X+82, Y+33
+Prize: X=17126, Y=1844
+
+Button A: X+15, Y+46
+Button B: X+52, Y+29
+Prize: X=14512, Y=8557
+
+Button A: X+51, Y+19
+Button B: X+17, Y+57
+Prize: X=4573, Y=2565
+
+Button A: X+16, Y+84
+Button B: X+43, Y+29
+Prize: X=2326, Y=2374
+
+Button A: X+21, Y+80
+Button B: X+52, Y+12
+Prize: X=2872, Y=11268
+
+Button A: X+16, Y+56
+Button B: X+42, Y+20
+Prize: X=1218, Y=17444
+
+Button A: X+43, Y+14
+Button B: X+25, Y+38
+Prize: X=2364, Y=11092
+
+Button A: X+34, Y+16
+Button B: X+42, Y+65
+Prize: X=19300, Y=16358
+
+Button A: X+12, Y+47
+Button B: X+68, Y+29
+Prize: X=17592, Y=3390
+
+Button A: X+38, Y+11
+Button B: X+55, Y+70
+Prize: X=4021, Y=1867
+
+Button A: X+33, Y+13
+Button B: X+14, Y+52
+Prize: X=8642, Y=16058
+
+Button A: X+74, Y+27
+Button B: X+12, Y+54
+Prize: X=5318, Y=5265
+
+Button A: X+28, Y+44
+Button B: X+38, Y+11
+Prize: X=11126, Y=12365
+
+Button A: X+34, Y+56
+Button B: X+44, Y+20
+Prize: X=14102, Y=5556
+
+Button A: X+75, Y+85
+Button B: X+53, Y+16
+Prize: X=6607, Y=5549
+
+Button A: X+81, Y+20
+Button B: X+35, Y+57
+Prize: X=2908, Y=3281
+
+Button A: X+13, Y+30
+Button B: X+41, Y+19
+Prize: X=10899, Y=10340
+
+Button A: X+11, Y+25
+Button B: X+64, Y+22
+Prize: X=18766, Y=8966
+
+Button A: X+57, Y+15
+Button B: X+17, Y+42
+Prize: X=14691, Y=8777
+
+Button A: X+19, Y+29
+Button B: X+72, Y+16
+Prize: X=7014, Y=3194
+
+Button A: X+22, Y+57
+Button B: X+44, Y+21
+Prize: X=15632, Y=19217
+
+Button A: X+48, Y+94
+Button B: X+86, Y+37
+Prize: X=11514, Y=11115
+
+Button A: X+11, Y+53
+Button B: X+57, Y+22
+Prize: X=8712, Y=5709
+
+Button A: X+92, Y+23
+Button B: X+12, Y+81
+Prize: X=7868, Y=7661
+
+Button A: X+52, Y+79
+Button B: X+63, Y+22
+Prize: X=5604, Y=2322
+
+Button A: X+20, Y+51
+Button B: X+95, Y+41
+Prize: X=9500, Y=8125
+
+Button A: X+24, Y+85
+Button B: X+68, Y+46
+Prize: X=7808, Y=9339
+
+Button A: X+16, Y+58
+Button B: X+83, Y+72
+Prize: X=2007, Y=4300
+
+Button A: X+86, Y+16
+Button B: X+31, Y+75
+Prize: X=7780, Y=5186
+
+Button A: X+21, Y+59
+Button B: X+89, Y+41
+Prize: X=2578, Y=3062
+
+Button A: X+62, Y+13
+Button B: X+34, Y+86
+Prize: X=5006, Y=6334
+
+Button A: X+75, Y+86
+Button B: X+80, Y+11
+Prize: X=6665, Y=1749
+
+Button A: X+20, Y+55
+Button B: X+59, Y+47
+Prize: X=2643, Y=3004
diff --git a/2024/day13/input.txt.h b/2024/day13/input.txt.h
new file mode 100644
index 0000000..ed5938c
--- /dev/null
+++ b/2024/day13/input.txt.h
@@ -0,0 +1,15 @@
+#pragma once
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+extern uint32_t _binary_2024_day13_input_txt_start __asm("_binary_2024_day13_input_txt_start");
+extern uint32_t _binary_2024_day13_input_txt_end __asm("_binary_2024_day13_input_txt_end");
+extern uint32_t _binary_2024_day13_input_txt_size __asm("_binary_2024_day13_input_txt_size");
+
+#ifdef __cplusplus
+}
+#endif
diff --git a/2024/day13/sample1.txt b/2024/day13/sample1.txt
new file mode 100644
index 0000000..912f482
--- /dev/null
+++ b/2024/day13/sample1.txt
@@ -0,0 +1,15 @@
+Button A: X+94, Y+34
+Button B: X+22, Y+67
+Prize: X=8400, Y=5400
+
+Button A: X+26, Y+66
+Button B: X+67, Y+21
+Prize: X=12748, Y=12176
+
+Button A: X+17, Y+86
+Button B: X+84, Y+37
+Prize: X=7870, Y=6450
+
+Button A: X+69, Y+23
+Button B: X+27, Y+71
+Prize: X=18641, Y=10279
diff --git a/2024/day13/sample1.txt.h b/2024/day13/sample1.txt.h
new file mode 100644
index 0000000..67ffe0f
--- /dev/null
+++ b/2024/day13/sample1.txt.h
@@ -0,0 +1,15 @@
+#pragma once
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+extern uint32_t _binary_2024_day13_sample1_txt_start __asm("_binary_2024_day13_sample1_txt_start");
+extern uint32_t _binary_2024_day13_sample1_txt_end __asm("_binary_2024_day13_sample1_txt_end");
+extern uint32_t _binary_2024_day13_sample1_txt_size __asm("_binary_2024_day13_sample1_txt_size");
+
+#ifdef __cplusplus
+}
+#endif
diff --git a/2024/day13/solution.c b/2024/day13/solution.c
new file mode 100644
index 0000000..a0064c9
--- /dev/null
+++ b/2024/day13/solution.c
@@ -0,0 +1,124 @@
+#include <stdint.h>
+
+#include "linear_algebra.h"
+#include "parse.h"
+
+struct button {
+  int x;
+  int y;
+};
+
+struct prize {
+  int x;
+  int y;
+};
+
+struct claw_machine {
+  struct {
+    struct button a;
+    struct button b;
+  } button;
+  struct prize prize;
+};
+
+static const char * parse_button(const char * input, char c,
+                                 int * x, int * y)
+{
+  input = parse_match(input, "Button ");
+  input = parse_skip(input, c);
+  input = parse_match(input, ": X+");
+  input = parse_base10(input, x);
+  input = parse_match(input, ", Y+");
+  input = parse_base10(input, y);
+  input = parse_skip(input, '\n');
+  return input;
+}
+
+static const char * parse_prize(const char * input,
+                                int * x, int * y)
+{
+  input = parse_match(input, "Prize: X=");
+  input = parse_base10(input, x);
+  input = parse_match(input, ", Y=");
+  input = parse_base10(input, y);
+  input = parse_skip(input, '\n');
+  return input;
+}
+
+static const char * parse_claw_machine(const char * input,
+                                       struct claw_machine * cm)
+{
+  input = parse_button(input, 'A', &cm->button.a.x, &cm->button.a.y);
+  input = parse_button(input, 'B', &cm->button.b.x, &cm->button.b.y);
+  input = parse_prize(input, &cm->prize.x, &cm->prize.y);
+  return input;
+}
+
+static bool is_integral(double x)
+{
+  int64_t ix = x;
+  double dx = ix;
+  double diff = dx - x;
+  return (diff < 0.00000001) && (diff > -0.00000001);
+}
+
+int64_t _2024_day13_part1(const char * input, int length)
+{
+  const char * end = input + length;
+
+  int cost = 0;
+
+  while (input < end) {
+    struct claw_machine cm;
+    input = parse_claw_machine(input, &cm);
+
+    double ax = cm.button.a.x;
+    double ay = cm.button.a.y;
+    double bx = cm.button.b.x;
+    double by = cm.button.b.y;
+    double x = cm.prize.x;
+    double y = cm.prize.y;
+
+    struct double2 r = cramers_rule_2x2(ax, bx, x,
+                                        ay, by, y);
+    if (is_integral(r.x) && is_integral(r.y)) {
+      int a = (int)r.x;
+      int b = (int)r.y;
+      cost += a * 3 + b;
+    }
+  }
+  return cost;
+}
+
+int64_t _2024_day13_part2(const char * input, int length)
+{
+  const char * end = input + length;
+
+  int64_t cost = 0;
+
+  while (input < end) {
+    struct claw_machine cm;
+    input = parse_claw_machine(input, &cm);
+
+    double ax = cm.button.a.x;
+    double ay = cm.button.a.y;
+    double bx = cm.button.b.x;
+    double by = cm.button.b.y;
+    double x = cm.prize.x;
+    double y = cm.prize.y;
+    x += 10000000000000;
+    y += 10000000000000;
+
+    struct double2 r = cramers_rule_2x2(ax, bx, x,
+                                        ay, by, y);
+    if (r.x == infinity || r.y == infinity) {
+      continue;
+    }
+    if (is_integral(r.x) && is_integral(r.y)) {
+      int64_t a = (int64_t)(r.x);
+      int64_t b = (int64_t)(r.y);
+      cost += a * 3 + b;
+    }
+  }
+  return cost;
+}
diff --git a/Makefile b/Makefile
index 20566ab..75f0137 100644
--- a/Makefile
+++ b/Makefile
@@ -1,12 +1,13 @@
 all: $(patsubst %.cpp,%.elf,$(wildcard example/*.cpp))
 
-OPT = -Og
+OPT = -O0
 
 MAKEFILE_PATH := $(patsubst %/,%,$(dir $(abspath $(firstword $(MAKEFILE_LIST)))))
 CFLAGS += -I$(MAKEFILE_PATH)
 CFLAGS += -I$(MAKEFILE_PATH)/dreamcast/
 CFLAGS += -Wno-char-subscripts
 LIB ?= $(MAKEFILE_PATH)/dreamcast
+
 CARCH = -m4 -ml
 
 include dreamcast/base.mk
diff --git a/aoc.mk b/aoc.mk
index 94ba4b9..07f2497 100644
--- a/aoc.mk
+++ b/aoc.mk
@@ -7,7 +7,8 @@ OBJ = \
 	cartesian.o \
 	array.o \
 	memory.o \
-	heap.o
+	heap.o \
+	linear_algebra.o
 
 DREAMCAST_OBJ = \
 	runner_dreamcast.o \
@@ -25,7 +26,10 @@ DREAMCAST_OBJ = \
 	libgcc/_moddi3.o \
 	libgcc/_udiv_qrnnd_16.o \
 	libgcc/_clz.o \
-	libgcc/_div_table.o
+	libgcc/_div_table.o \
+	libgcc/_fixdfdi.o \
+	libgcc/_fixunsdfdi.o \
+	libgcc/_floatdidf.o
 
 include solutions.mk
 
diff --git a/double.h b/double.h
new file mode 100644
index 0000000..f5c1d58
--- /dev/null
+++ b/double.h
@@ -0,0 +1,18 @@
+#pragma once
+
+#include <stdint.h>
+
+#define infinity (__builtin_inf())
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct double2 {
+  double x;
+  double y;
+};
+
+#ifdef __cplusplus
+}
+#endif
diff --git a/input_dreamcast.inc b/input_dreamcast.inc
index 90fc0d0..c5652e9 100644
--- a/input_dreamcast.inc
+++ b/input_dreamcast.inc
@@ -33,6 +33,8 @@
 #include "2024/day12/sample1.txt.h"
 #include "2024/day12/sample2.txt.h"
 #include "2024/day12/input.txt.h"
+#include "2024/day13/sample1.txt.h"
+#include "2024/day13/input.txt.h"
 
 static struct start_size sample[][2] = {
   {
@@ -131,6 +133,12 @@ static struct start_size sample[][2] = {
     { (  char *)&_binary_2024_day12_sample2_txt_start,
       (uint32_t)&_binary_2024_day12_sample2_txt_size   },
   },
+  {
+    { (  char *)&_binary_2024_day13_sample1_txt_start,
+      (uint32_t)&_binary_2024_day13_sample1_txt_size   },
+    { (  char *)&_binary_2024_day13_sample1_txt_start,
+      (uint32_t)&_binary_2024_day13_sample1_txt_size   },
+  },
 };
 
 static struct start_size input[] = {
@@ -166,4 +174,6 @@ static struct start_size input[] = {
     (uint32_t)&_binary_2024_day11_input_txt_size   },
   { (  char *)&_binary_2024_day12_input_txt_start,
     (uint32_t)&_binary_2024_day12_input_txt_size   },
+  { (  char *)&_binary_2024_day13_input_txt_start,
+    (uint32_t)&_binary_2024_day13_input_txt_size   },
 };
diff --git a/linear_algebra.c b/linear_algebra.c
new file mode 100644
index 0000000..dd9d258
--- /dev/null
+++ b/linear_algebra.c
@@ -0,0 +1,56 @@
+#include "linear_algebra.h"
+
+#include "printf.h"
+//#include <stdio.h>
+
+double determinant_2x2(double a, double b,
+                       double c, double d)
+{
+  /*
+    a b
+    c d
+   */
+
+  return a * d - b * c;
+}
+
+/*
+5550.00 450000000444000.00 600000000222000.00
+81081081161.08 108108108148.11
+
+-3876.00 -460000000548084.00 -400000000524792.00
+118679050709.00 103199174542.00
+
+-6595.00 -470000000250610.00 -690000000567170.00
+71266110727.92 104624715779.71
+
+4278.00 440000001045978.00 460000000280508.00
+102851800151.00 107526881786.00
+*/
+
+union di {
+  double d;
+  int64_t i;
+};
+
+static int64_t raw_double(double n)
+{
+  union di di;
+  di.d = n;
+  return di.i;
+}
+
+struct double2 cramers_rule_2x2(double a1, double b1, double c1,
+                                double a2, double b2, double c2)
+{
+  double denom = determinant_2x2(a1, b1,
+                                 a2, b2);
+
+  double x_numer = determinant_2x2(c1, b1,
+                                   c2, b2);
+
+  double y_numer = determinant_2x2(a1, c1,
+                                   a2, c2);
+
+  return (struct double2){x_numer / denom, y_numer / denom};
+}
diff --git a/linear_algebra.h b/linear_algebra.h
new file mode 100644
index 0000000..4e2a04a
--- /dev/null
+++ b/linear_algebra.h
@@ -0,0 +1,19 @@
+#pragma once
+
+#include <stdint.h>
+
+#include "double.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+double determinant_2x2(double a, double b,
+                       double c, double d);
+
+struct double2 cramers_rule_2x2(double a1, double b1, double c1,
+                                double a2, double b2, double c2);
+
+#ifdef __cplusplus
+}
+#endif
diff --git a/runner.c b/runner.c
index ab4d4c6..aafa3ad 100644
--- a/runner.c
+++ b/runner.c
@@ -38,7 +38,7 @@ bool runner_tick(struct runner_state * runner_state)
   int year = solution[ix].year;
   int day = solution[ix].day;
 
-  if (year != 2023 || day != 24) {
+  if (year != 2024 || day != 13) {
     return false;
   }
 
diff --git a/runner.inc b/runner.inc
index 2281ead..a6ac2dd 100644
--- a/runner.inc
+++ b/runner.inc
@@ -33,6 +33,8 @@ int64_t _2024_day11_part1(const char * input, int length);
 int64_t _2024_day11_part2(const char * input, int length);
 int64_t _2024_day12_part1(const char * input, int length);
 int64_t _2024_day12_part2(const char * input, int length);
+int64_t _2024_day13_part1(const char * input, int length);
+int64_t _2024_day13_part2(const char * input, int length);
 
 struct day_funcs solution[] = {
   {
@@ -115,4 +117,9 @@ struct day_funcs solution[] = {
     {_2024_day12_part1, _2024_day12_part2},
     NULL,
   },
+  {
+    2024, 13,
+    {_2024_day13_part1, _2024_day13_part2},
+    NULL,
+  },
 };
diff --git a/solutions.mk b/solutions.mk
index 7b9f6f9..487ecb8 100644
--- a/solutions.mk
+++ b/solutions.mk
@@ -50,4 +50,7 @@ DAY_OBJ = \
 	2024/day12/sample1.txt.o \
 	2024/day12/sample2.txt.o \
 	2024/day12/input.txt.o \
-	2024/day12/solution.o
+	2024/day12/solution.o \
+	2024/day13/sample1.txt.o \
+	2024/day13/input.txt.o \
+	2024/day13/solution.o