diff --git a/2024/Day3/.clang-format b/2024/Day3/.clang-format
new file mode 100644
index 0000000..3773a50
--- /dev/null
+++ b/2024/Day3/.clang-format
@@ -0,0 +1,6 @@
+BasedOnStyle: LLVM
+IndentWidth: 4
+ColumnLimit: 100
+PointerAlignment: Right
+AlignAfterOpenBracket: BlockIndent
+AlignArrayOfStructures: Left
diff --git a/2024/Day3/Makefile b/2024/Day3/Makefile
new file mode 100644
index 0000000..9d1e7e6
--- /dev/null
+++ b/2024/Day3/Makefile
@@ -0,0 +1,17 @@
+CC = gcc
+CC_FLAGS = -Wall -Wextra -Werror -Wpedantic -Wno-unused-parameter -Wno-unused-variable -Wno-unused-function
+CC_LINK_FLAGS =
+
+.PHONY: all run clean
+all: run
+
+run: build
+	./target/main.o
+
+build: src/main.c
+	mkdir -p target
+	$(CC) -o target/main.o src/main.c $(CC_FLAGS) $(CC_LINK_FLAGS)
+	chmod u+x target/main.o
+
+clean:
+	rm -r target/*
diff --git a/2024/Day3/src/main.c b/2024/Day3/src/main.c
index e69de29..eb89888 100644
--- a/2024/Day3/src/main.c
+++ b/2024/Day3/src/main.c
@@ -0,0 +1,155 @@
+#include <regex.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+int get_max_line_length(char *filename);
+int *get_numbers_from_mul(const char *s, int start, int end);
+void init_regex(regex_t *regex, char *patter);
+
+int main(void) {
+    regex_t mul_regex;
+    regex_t do_regex;
+    regex_t dont_regex;
+    int reti;
+
+    int do_start, dont_start = -1;
+    char msgbuf[100];
+    FILE *file;
+    char filename[] = "input.txt";
+    const int MAX_LINE_LENGTH = get_max_line_length(filename);
+    char *buffer = malloc(MAX_LINE_LENGTH * sizeof(char));
+    int sum = 0;
+    int is_enabled = 1;
+    regmatch_t match[1];
+    regmatch_t do_dont_match[1];
+
+    file = fopen(filename, "r");
+
+    if (file == NULL) {
+        perror("Error opening file");
+        return 1;
+    }
+
+    init_regex(&mul_regex, "mul\\([0-9]{1,3},[0-9]{1,3}\\)");
+    init_regex(&do_regex, "do\\(\\)");
+    init_regex(&dont_regex, "don't\\(\\)");
+
+    while (fgets(buffer, MAX_LINE_LENGTH, file) != NULL) {
+        const char *search_start = buffer;
+        while ((reti = regexec(&mul_regex, search_start, 1, match, 0)) == 0) {
+            int match_start = match[0].rm_so;
+            int match_end = match[0].rm_eo;
+
+            reti = regexec(&do_regex, search_start, 1, do_dont_match, 0);
+            if (!reti) {
+                do_start = do_dont_match[0].rm_so;
+            } else {
+                do_start = strlen(search_start);
+            }
+
+            reti = regexec(&dont_regex, search_start, 1, do_dont_match, 0);
+            if (!reti) {
+                dont_start = do_dont_match[0].rm_so;
+            }
+
+            if (do_start < match_start && (dont_start > match_start || dont_start < do_start)) {
+                is_enabled = 1;
+            }
+
+            if (dont_start < match_start && (do_start > match_start || do_start < dont_start)) {
+                is_enabled = 0;
+            }
+
+            if (is_enabled) {
+                int *numbers = get_numbers_from_mul(search_start, match_start, match_end);
+
+                sum += numbers[0] * numbers[1];
+
+                free(numbers);
+            }
+
+            if (is_enabled) {
+                search_start += match_end;
+            } else {
+                if (do_start == 0) {
+                    do_start = 1;
+                }
+                search_start += do_start;
+            }
+        }
+    }
+
+    printf("%d\n", sum);
+
+    fclose(file);
+    regfree(&mul_regex);
+    return 0;
+}
+
+int get_max_line_length(char *filename) {
+    FILE *file = fopen(filename, "r");
+
+    if (file == NULL) {
+        perror("Error opening file");
+        return -1;
+    }
+
+    int CUR_MAX = 4095;
+    char *buffer = (char *)malloc(sizeof(char) * CUR_MAX);
+    int length = 0;
+    char ch = ' ';
+
+    while ((ch != '\n') && (ch != EOF)) {
+        if (length == CUR_MAX) {
+            CUR_MAX *= 2;
+            buffer = realloc(buffer, CUR_MAX);
+        }
+        ch = getc(file);
+        buffer[length] = ch;
+        length++;
+    }
+
+    free(buffer);
+    fclose(file);
+    return CUR_MAX;
+}
+
+void init_regex(regex_t *regex, char *pattern) {
+    int reti = regcomp(regex, pattern, REG_EXTENDED);
+    if (reti) {
+        fprintf(stderr, "Could not compile regex\n");
+        exit(1);
+    }
+}
+
+int *get_numbers_from_mul(const char *s, int start, int end) {
+    char *num1 = malloc(3);
+    char *num2 = malloc(3);
+    int *numbers = malloc(2 * sizeof(int));
+
+    int is_first = 1;
+    int current_number_index = 0;
+    for (int i = start; i < end; i++) {
+        char current = s[i];
+        if (current >= '0' && current <= '9') {
+            if (is_first) {
+                num1[current_number_index] = current;
+                current_number_index++;
+            } else {
+                num2[current_number_index] = current;
+                current_number_index++;
+            }
+        } else if (current == ',') {
+            is_first ^= 1;
+            current_number_index = 0;
+        }
+    }
+
+    numbers[0] = atoi(num1);
+    numbers[1] = atoi(num2);
+    free(num1);
+    free(num2);
+
+    return numbers;
+}