diff --git a/include/alg.h b/include/alg.h
index b3ebcd7..fb23f49 100644
--- a/include/alg.h
+++ b/include/alg.h
@@ -1,7 +1,10 @@
-// Copyright 2021 NNTU-CS
+// Copyright 2024 Nazyrov A.A.
+
 #ifndef INCLUDE_ALG_H_
 #define INCLUDE_ALG_H_
 
+#include <cstdint>
+
 uint64_t factorial(uint8_t n);
 
 #endif  // INCLUDE_ALG_H_
diff --git a/src/alg.cpp b/src/alg.cpp
index 6e34e74..d07f901 100644
--- a/src/alg.cpp
+++ b/src/alg.cpp
@@ -1,6 +1,11 @@
-// Copyright 2026 NNTU-CS
-#include <cstdint>
+// Copyright 2024 Nazyrov A.A.
+
+#include "alg.h"
 
 uint64_t factorial(uint8_t n) {
-  return 1;
+    uint64_t result = 1;
+    for (uint8_t i = 2; i <= n; ++i) {
+        result *= i;
+    }
+    return result;
 }