diff --git a/day18p1/Makefile b/day18p1/Makefile
new file mode 100644
index 0000000..79bbc11
--- /dev/null
+++ b/day18p1/Makefile
@@ -0,0 +1,12 @@
+CFLAGS := -O3 -Wall -Wextra -std=c17 -D_GNU_SOURCE
+
+.PHONY: all
+all: main out/
+
+.PHONY: clean
+clean:
+	rm -f main out/*
+
+out/:
+	mkdir -p $@
+	touch $@/.gitkeep
diff --git a/day18p1/input b/day18p1/input
new file mode 100644
index 0000000..eb3c596
--- /dev/null
+++ b/day18p1/input
@@ -0,0 +1,50 @@
+........#.##..#|#|.#.....|......#..#.|..##..||.#..
+#|##.|||.|..|||......|.##.#|#|....||#.#...#...#..#
+..##...#|#..|#.|..#||#...|#....|#...#|#.|.||...|..
+.....#|||.|.#...###|....|#..#.#.#.|..#||#|....|#.|
+....|.....#.||.#..#...#|....|||..#....##...|..|.#|
+||...|###..|..|||..|#.##|.####.#...|.||.|....|.##.
+..#.#.###..||......#|#|.|....#|.#|.|...#....#...#|
+.|..||||||...#.##..|.#||.#|##|..#.#..##..#...|#...
+.|.....||...#.#|.##|..|.##||..#.#..|..#.#.#..|.#|.
+||...|#........#.|..##|.|..#...#...#|#|..||.|....#
+#||.|.|..|.......##....|..#||#.#|.|||......|..||..
+.....#.|||.....|.#.#.......#.|..#.|.....|.|.#...#.
+...#.##.#.||#.#|.#.##..#.||#.#.#|#.||.||.|......#.
+|.|...#|.|####|.|..#.#|....|......|....|...||#||..
+.#...#.#......|...#.....|.....|.#|...##|||...#.|#.
+||##.#...#.|...##..##.||#...#|...|##.##...#||..#|.
+|.|#.||..|##.|.#.|..#..|.##.#.......#...|....||...
+.|.......#..##...|.|..|#.#....|#|..##|#|.##|.|.|#.
+.|....|.#|||#.#..#..|||.....||...#|.#..|..#.#...#.
+...#..###.#|.##||.#.|.||###..|..|#.|#..||......||.
+..##.......##|.....#...|#|..##|.#.|||.|#....|##...
+#...#|##|......##|...|#..#.|..##..#..#.|##.##|#..#
+|.#|.....|..#...|....|...#....#|..#.....||...|#|.|
+##...#.....#.....|#|.......|....####.#..##.|.##...
+.....|...|#|#..|#|.|..##.|..|....##..||.#...|..|.|
+.|..|....##.||||.##|.#...|..|#|.#.|####.|..|##.#..
+#.........|##.#|..##|...|........|..|....|..#...##
+.#.|...#...#...|.|...|..|.#.|....#..|.|..|..#|....
+.....#.....#|.#....|....##...##....###....#.|...|.
+||.....|.|.##|.##||.#|#.##|.#..|#####|...|...||#.#
+...#||....#.....##.|##|.##|#.##.#|.|.....#........
+..##.....||..#..#.|..##...#.|.|.|.|...|.#.|..|....
+|##..|..........##..#|...|......||.#....#....|..#.
+...#..|.#.|...|.##|.##..##..|.|....#||#|##..||||..
+#...##......|..|#...#.#.|#||..#...|.#...|..###.||.
+|#.......|#.|##|....|.....#..||.|#|#...#|....|..#|
+.|.....#|##.|.#...#..#||#.....|....#||.#|.##.##.#|
+|#..###..#..|#.....##...||.|.|.#.#|.||..||.||#|#..
+||||#....|#..|.|...|...||....|...#....#.##...#|...
+...||##||#......|#.#..#..|.....|...#..#|...#...|||
+.|#.|.|....|...#.....|#....|..#.#...#...||..##|..|
+||#.|##.|...|.##......##|#..#..#.#.#.....|#|##.##.
+|.#.....||.....#.#...|...|..|#|..|..#...|....|...|
+###..#.#......#|..#....#......|##.##....|||.|..#|.
+..#.|.#...#..|#####|.....##.|.|#......|..||.#|....
+.#||.|.##..#.|..##......|..|.|#..|.....#.....|#|..
+|##.#......#.#.#.#|||#|....#...#.|.........|||.#..
+|......||.|..#.|#||...||.#.#.##..#..#.#....#.#..#|
+#.|..##.....#..|...|#...#...|.......|.|..|#|......
+##...#....#..#..#....|...#|#.||.|...|.#..###|##|.|
diff --git a/day18p1/main.c b/day18p1/main.c
new file mode 100644
index 0000000..49c7809
--- /dev/null
+++ b/day18p1/main.c
@@ -0,0 +1,243 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdint.h>
+#include <time.h>
+
+struct size2d {
+    unsigned w;
+    unsigned h;
+};
+
+struct buffer {
+    char *data;
+    size_t len;
+    size_t alloc;
+};
+
+void *xrealloc(void *ptr, size_t size)
+{
+    void *res = realloc(ptr, size);
+    if (!res) {
+        perror("realloc");
+        exit(1);
+    }
+    return res;
+}
+
+struct buffer buffer_alloc()
+{
+    struct buffer buffer;
+    buffer.len = 0;
+    buffer.alloc = 0x10;
+    buffer.data = xrealloc(NULL, buffer.alloc);
+    return buffer;
+}
+
+void buffer_append(struct buffer *buffer, char c)
+{
+    if (buffer->alloc <= buffer->len) {
+        buffer->alloc *= 2;
+        buffer->data = xrealloc(buffer->data, buffer->alloc);
+    }
+    buffer->data[buffer->len++] = c;
+}
+
+char *parse_acres(const char *fname, struct size2d *size)
+{
+    FILE *f = fopen(fname, "r");
+    if (!f) {
+        perror(fname);
+        return NULL;
+    }
+
+    struct buffer buffer = buffer_alloc();
+    size->w = 0;
+    size->h = 0;
+
+    unsigned width = 0;
+    int c;
+
+    flockfile(f);
+    while ((c = getc_unlocked(f)) != EOF) {
+        if (c == '\n') {
+            if (!size->w) {
+                size->w = width;
+            } else {
+                if (size->w != width) {
+                    fprintf(stderr, "ERROR: Not each line has the same width\n");
+                    goto error;
+                }
+            }
+            width = 0;
+            size->h++;
+            continue;
+        }
+
+        if (c != '.' && c != '|' && c != '#') {
+            fprintf(stderr, "ERROR: Unknown character: '%c'\n", c);
+            goto error;
+        }
+
+        buffer_append(&buffer, c);
+        width++;
+    }
+    funlockfile(f);
+    fclose(f);
+
+    return realloc(buffer.data, buffer.len);
+
+error:
+    funlockfile(f);
+    fclose(f);
+    free(buffer.data);
+    return NULL;
+}
+
+void advance_frame(char *acres, char *next, const struct size2d size)
+{
+    for (unsigned y = 0; y < size.h; y++) {
+        for (unsigned x = 0; x < size.w; x++) {
+            char *a = next + y * size.w + x;
+
+            char surrounding[8] = {'\0'};
+            if (y > 0) surrounding[0] = acres[(y - 1) * size.w + x];
+            if (x > 0) surrounding[1] = acres[y * size.w + (x - 1)];
+            if (y + 1 < size.h) surrounding[2] = acres[(y + 1) * size.w + x];
+            if (x + 1 < size.w) surrounding[3] = acres[y * size.w + (x + 1)];
+            if (y > 0 && x + 1 < size.w)
+                surrounding[4] = acres[(y - 1) * size.w + (x + 1)];
+            if (y > 0 && x > 0)
+                surrounding[5] = acres[(y - 1) * size.w + (x - 1)];
+            if (y + 1 < size.h && x > 0)
+                surrounding[6] = acres[(y + 1) * size.w + (x - 1)];
+            if (y + 1 < size.h && x + 1 < size.w)
+                surrounding[7] = acres[(y + 1) * size.w + (x + 1)];
+
+            unsigned tally = 0;
+            unsigned tally2 = 0;
+            char new = 0;
+
+            switch (*a) {
+            case '.':
+            case '|':
+                new = (*a == '.' ? '|' : '#');
+                for (char *c = surrounding; c < surrounding + 8; c++) {
+                    if (*c == new) tally++;
+                }
+                if (tally >= 3) *a = new;
+                break;
+            case '#':
+                for (char *c = surrounding; c < surrounding + 8; c++) {
+                    if (*c == '#') tally++;
+                    if (*c == '|') tally2++;
+                }
+                if (!(tally >= 1 && tally2 >= 1)) *a = '.';
+                break;
+            }
+        }
+    }
+}
+
+int render_bitmap(const char *fname, const char *acres, const struct size2d size)
+{
+    FILE *f = fopen(fname, "w");
+    if (!f) {
+        perror(fname);
+        return 1;
+    }
+
+    flockfile(f);
+    fprintf(f, "P6\n%u %u\n255\n", size.w, size.h);
+
+    for (unsigned y = 0; y < size.h; y++) {
+        for (unsigned x = 0; x < size.w; x++) {
+            char color[3] = {255};
+
+            switch (acres[y * size.w + x]) {
+            case '.':
+                // Yellow
+                color[0] = 205;
+                color[1] = 255;
+                color[2] = 110;
+                break;
+            case '|':
+                // Green
+                color[0] = 0;
+                color[1] = 255;
+                color[2] = 0;
+                break;
+            case '#':
+                // Brown
+                color[0] = 192;
+                color[1] = 125;
+                color[2] = 0;
+                break;
+            }
+
+            fwrite_unlocked(color, 3, 1, f);
+        }
+    }
+
+    funlockfile(f);
+    fclose(f);
+    return 0;
+}
+
+int main(int argc, char *argv[])
+{
+    struct size2d size;
+    char *acres = parse_acres("input", &size);
+    if (!acres) return 1;
+
+    unsigned minutes = 10;
+    int render = 0;
+    if (argc > 1) minutes = strtol(argv[1], NULL, 0);
+    if (argc > 2 && strcmp(argv[2], "-render") == 0) render = 1;
+
+    char *next = xrealloc(NULL, size.w * size.h);
+    memcpy(next, acres, size.w * size.h);
+
+    char *fname = NULL;
+    clock_t start = clock();
+    for (unsigned i = 0; i <= minutes; i++) {
+        if (i != 0) {
+            advance_frame(acres, next, size);
+            memcpy(acres, next, size.w * size.h);
+
+            if (i % 10000 == 0) {
+                double framespers = 10000 / ((double)(clock() - start) / CLOCKS_PER_SEC);
+                unsigned eta = (double)(minutes - i) / framespers;
+                fprintf(stderr, "Progress: %.2f%% (speed: %.2f frames/s, ETA: %u:%u:%u)\n",
+                        (double)i / minutes * 100, framespers,
+                        eta / 60 / 60, (eta / 60) % 60, eta % 60);
+                start = clock();
+            }
+        }
+
+        if (render) {
+            if (asprintf(&fname, "out/frame%04u.ppm", i) == -1) {
+                perror("asprintf");
+                break;
+            }
+            if (render_bitmap(fname, acres, size)) break;
+            free(fname);
+        }
+    }
+
+    unsigned wood = 0;
+    unsigned lumber = 0;
+    for (unsigned y = 0; y < size.h; y++) {
+        for (unsigned x = 0; x < size.w; x++) {
+            char c = acres[y * size.w + x];
+            if (c == '|') wood++;
+            if (c == '#') lumber++;
+        }
+    }
+
+    printf("Resource value: %u\n", wood * lumber);
+
+    free(next);
+    free(acres);
+    return 0;
+}
diff --git a/day18p1/makegif.sh b/day18p1/makegif.sh
new file mode 100755
index 0000000..5df75d9
--- /dev/null
+++ b/day18p1/makegif.sh
@@ -0,0 +1,2 @@
+#!/bin/sh
+convert -monitor -resize 1000% -filter point -delay 5 -loop 0 out/*.ppm out.gif
diff --git a/day18p1/out.gif b/day18p1/out.gif
new file mode 100644
index 0000000..f05e320
Binary files /dev/null and b/day18p1/out.gif differ
diff --git a/day18p1/out/.gitkeep b/day18p1/out/.gitkeep
new file mode 100644
index 0000000..e69de29