diff --git a/buggy.py b/buggy.py
--- a/buggy.py
+++ b/buggy.py
@@ -24,7 +24,7 @@
         for cha in s:
             ct2 += 1
             if cha != "a":
-                ans += chr(ord(cha) - 2)
+                ans += chr(ord(cha) - 1)
                 change = True  # record operation at least once.
                 continue
             else:
