diff --git a/buggy.py b/buggy.py
--- a/buggy.py
+++ b/buggy.py
@@ -12,7 +12,7 @@
         com = ""
         while num > 0:
             if num % 2 == 1:
-                com += not_defined_variable
+                com += "0"
             else:
                 com += "1"
             num = num // 2
