fix string

app.py

@@ -26,7 +26,7 @@ def generate_prompt(instruction, input=None, history=None):
         for pair in history:
             if pair[0] is not None and pair[1] is not None and len(pair[1]) > 0:
                 input += f"{pair[0]},{pair[1]},"
-        input = input[-1] + f". {instruction}"
+        input = input[:-1] + f". {instruction}"
         instruction = "Generate a Response using the following query."
     if input and len(input) > 0:
         input = (