diff --git a/leetcode/20.py b/leetcode/20.py
index e4eb84d..26da62c 100644
--- a/leetcode/20.py
+++ b/leetcode/20.py
@@ -10,6 +10,7 @@ class Solution:
             try:
                 stack_top = stack.pop()
             except IndexError:
+                stack.append(i)
                 continue
 
             try: