diff --git a/src/index.js b/src/index.js
index f16abeb..2175e4c 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,5 +1,7 @@
 const factorial = (number) => {
-    
-  }
+  if (number < 0) return;
+  if (number === 0) return 1;
+  return number * factorial(number - 1);
+};
 
-  module.exports = factorial;
\ No newline at end of file
+module.exports = factorial;