diff --git a/day4.c b/day4.c
new file mode 100644
index 0000000..867b04e
--- /dev/null
+++ b/day4.c
@@ -0,0 +1,81 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/param.h>
+
+#include "aoc.h"
+
+typedef struct {
+	int from, to;
+} Range;
+
+typedef struct {
+	Range first;
+	Range second;
+} DoubleRange;
+
+typedef struct {
+	DoubleRange *ranges;
+	size_t count;
+} day4_Data;
+
+static inline void day4_parse_range(Range *range, char *s)
+{
+	range->from = atoi(strsep(&s, "-"));
+	range->to   = atoi(strsep(&s, "-"));
+}
+
+static void day4_parse_line(DoubleRange *double_range, char *line)
+{
+	char *line_copy = strdup(line);
+	char *line_copy_start = line_copy;
+	day4_parse_range(&double_range->first, strsep(&line_copy, ","));
+	day4_parse_range(&double_range->second, strsep(&line_copy, ","));
+	free(line_copy_start);
+}
+
+static void *day4_parse(char **lines, int line_count)
+{
+	day4_Data *data = calloc(1, sizeof(day4_Data));
+	DoubleRange *ranges = calloc(line_count, sizeof(DoubleRange));
+	data->ranges = ranges;
+	data->count = line_count;
+	for (size_t i = 0; i < line_count; i++) {
+		day4_parse_line(&data->ranges[i], lines[i]);
+	}
+	return data;
+}
+
+static int day4_part1(void *p)
+{
+	day4_Data *data = (day4_Data*)p;
+	int result = 0;
+	for (int i = 0; i < data->count; i++) {
+		Range *range1 = &data->ranges[i].first;
+		Range *range2 = &data->ranges[i].second;
+		if ((range1->from <= range2->from && range1->to >= range2->to) ||
+				(range2->from <= range1->from && range2->to >= range1->to)) {
+			result++;
+		}
+	}
+	return result;
+}
+
+static int day4_part2(void *p)
+{
+	day4_Data *data = (day4_Data*)p;
+	int result = 0;
+	for (int i = 0; i < data->count; i++) {
+		Range *range1 = &data->ranges[i].first;
+		Range *range2 = &data->ranges[i].second;
+		if ((range1->from <= range2->from && range1->to >= range2->to) ||
+				(range2->from <= range1->from && range2->to >= range1->to) ||
+				MIN(range1->to, range2->to) >= MAX(range1->from, range2->from)) {
+			result++;
+		}
+	}
+	return result;
+}
+
+
+ADD_SOLUTION(4, day4_parse, day4_part1, day4_part2);
diff --git a/main.c b/main.c
index 2d385ac..26d7a56 100644
--- a/main.c
+++ b/main.c
@@ -11,6 +11,7 @@
 #include "day1.c"
 #include "day2.c"
 #include "day3.c"
+#include "day4.c"
 
 Solution *find_solution(int day)
 {