diff --git a/src/index.js b/src/index.js
index 243d154..068873d 100644
--- a/src/index.js
+++ b/src/index.js
@@ -6,6 +6,14 @@
 
 const hammingDistance = (a, b) => {
     
+    if (a.length === b.length) {
+      const aArray = a.split('');
+      const bArray = b.split('');
+      return bArray.filter((letter, index) => aArray[index] !== letter).length
+    } else {
+      throw new Error("You must enter strings with the same length");
+    }
+    
   }
   
   module.exports = hammingDistance;
\ No newline at end of file