diff --git a/day11.c b/day11.c
new file mode 100644
index 0000000..12369cf
--- /dev/null
+++ b/day11.c
@@ -0,0 +1,187 @@
+#include <limits.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+
+#include "aoc.h"
+
+typedef enum {
+	MONKEY_OP_ADD,
+	MONKEY_OP_MUL,
+	MONKEY_OP_SQR
+} MONKEY_OP;
+
+typedef struct {
+	int *items;
+	int item_count;
+	MONKEY_OP op;
+	int op_value;
+	int test_value;
+	int test_true;
+	int test_false;
+} Monkey;
+
+typedef struct {
+	Monkey *monkeys;
+	int count;
+} day11_Data;
+
+static int count_char(char *str, char target)
+{
+	int count = 0;
+	for (int i = 0; i < strlen(str); i++) {
+		count += str[i] == target;
+	}
+	return count;
+}
+
+static void parse_items(char *items, int **result, int *result_count)
+{
+	int i = 0;
+	*result_count = count_char(items, ',')+1;
+	*result = malloc(*result_count * sizeof(int));
+	for (char *num = strtok(items, ","); num; num = strtok(NULL, ",")) {
+		(*result)[i] = atoi(num+1);
+		i++;
+	}
+}
+
+static void parse_operation(char *operation, MONKEY_OP *op, int *op_value)
+{
+	if (operation[4] == '+') {
+		*op = MONKEY_OP_ADD;
+		*op_value = atoi(operation + 6);
+	} else if (operation[4] == '*' && operation[6] == 'o') {
+		*op = MONKEY_OP_SQR;
+	} else {
+		*op = MONKEY_OP_MUL;
+		*op_value = atoi(operation + 6);
+	}
+}
+
+static inline void apply_operation(uint64_t *value, MONKEY_OP op, int op_value)
+{
+	switch (op) {
+	case MONKEY_OP_ADD:
+		*value += op_value;
+		break;
+	case MONKEY_OP_MUL:
+		*value *= op_value;
+		break;
+	case MONKEY_OP_SQR:
+		*value *= *value;
+		break;
+	default:
+		printf("abort: %d\n", op);
+		fflush(stdout);
+		abort();
+	}
+}
+
+static void *day11_parse(char **lines, int line_count)
+{
+	day11_Data *data = malloc(sizeof(day11_Data));
+	data->count = (line_count + 1)/7;
+	data->monkeys = malloc(data->count * sizeof(Monkey));
+
+	for (int i = 0; i < line_count; i+=7) {
+		Monkey *monkey = &data->monkeys[i/7];
+		char *starting_items = lines[i+1] + 17;
+		char *operation      = lines[i+2] + 19;
+		char *test_value     = lines[i+3] + 21;
+		char *test_true      = lines[i+4] + 29;
+		char *test_false     = lines[i+5] + 30;
+		parse_items(starting_items, &monkey->items, &monkey->item_count);
+		parse_operation(operation, &monkey->op, &monkey->op_value);
+		monkey->test_value = atoi(test_value);
+		monkey->test_true  = atoi(test_true);
+		monkey->test_false = atoi(test_false);
+	}
+
+	return data;
+}
+
+static uint64_t solve(day11_Data *data, int rounds, bool reduce_worry)
+{
+	int monkey_count = data->count;
+
+	int inspections[monkey_count];
+	for (int i = 0; i < data->count; i++) {
+		inspections[i] = 0;
+	}
+
+	int total_item_count = 0;
+	for (int i = 0; i < monkey_count; i++) {
+		total_item_count += data->monkeys[i].item_count;
+	}
+
+	size_t items[monkey_count][total_item_count];
+	size_t item_counts[monkey_count];
+	for (int i = 0; i < monkey_count; i++) {
+		Monkey *monkey = &data->monkeys[i];
+		item_counts[i] = monkey->item_count;
+		for (int j = 0; j < monkey->item_count; j++) {
+			items[i][j] = monkey->items[j];
+		}
+	}
+
+	int modulo = 1;
+	for (int i = 0; i < monkey_count; i++) {
+		modulo *= data->monkeys[i].test_value;
+	}
+
+	for (int round = 1; round <= rounds; round++) {
+		for (int i = 0; i < monkey_count; i++) {
+			Monkey *monkey = &data->monkeys[i];
+			for (int j = 0; j < item_counts[i]; j++) {
+				uint64_t item_worry = items[i][j];
+				apply_operation(&item_worry, monkey->op, monkey->op_value);
+				if (reduce_worry) {
+					item_worry /= 3;
+				} else {
+					item_worry %= modulo;
+				}
+
+				int target_monkey;
+				if (item_worry % monkey->test_value == 0) {
+					target_monkey = monkey->test_true;
+				} else {
+					target_monkey = monkey->test_false;
+				}
+
+				items[target_monkey][item_counts[target_monkey]++] = item_worry;
+			}
+
+			inspections[i] += item_counts[i];
+			item_counts[i] = 0;
+		}
+
+	}
+
+	uint64_t top_inspection1 = 0;
+	uint64_t top_inspection2 = 0;
+	for (int i = 0; i < monkey_count; i++) {
+		if (inspections[i] > top_inspection1) {
+			top_inspection2 = top_inspection1;
+			top_inspection1 = inspections[i];
+		} else if (inspections[i] > top_inspection2) {
+			top_inspection2 = inspections[i];
+		}
+	}
+
+	return top_inspection1*top_inspection2;
+}
+
+static void day11_part1(void *p)
+{
+	printf("%lu\n", solve(p, 20, true));
+}
+
+
+static void day11_part2(void *p)
+{
+	printf("%lu\n", solve(p, 10000, false));
+}
+
+ADD_SOLUTION(11, day11_parse, day11_part1, day11_part2);
diff --git a/main.c b/main.c
index f97e1dd..97e6a30 100644
--- a/main.c
+++ b/main.c
@@ -18,6 +18,7 @@
 #include "day8.c"
 #include "day9.c"
 #include "day10.c"
+#include "day11.c"
 
 Solution *find_solution(int day)
 {