diff --git a/leetcode/20.py b/leetcode/20.py
index 26da62c..e3c5727 100644
--- a/leetcode/20.py
+++ b/leetcode/20.py
@@ -16,6 +16,9 @@ class Solution:
             try:
                 if symbol_dict[stack_top] == i:
                     continue
+                else:
+                    stack.append(stack_top)
+
             except KeyError:
                 return False