diff --git a/src/alg.cpp b/src/alg.cpp
index 0f4a554..58bfb2e 100644
--- a/src/alg.cpp
+++ b/src/alg.cpp
@@ -1,5 +1,15 @@
-// Copyright 2021 NNTU-CS
+#include <iostream>
 
 int gcd(int a, int b) {
-	return 25;
+    while (b != 0) {
+        int perem = b;
+        b = a % b;
+        a = perem;
+    }
+    return a;
+}
+
+int main() {
+    std::cout << gcd(10,15) << std::endl;
+    return 0;
 }