class Solution:
    def minAddToMakeValid(self, S: str) -> int:
        # ToDO: Write Your Code Here.
        stack = []
        for i in S:
            if not stack or i=='(':
                stack.append(i)
            elif i == ')' and stack:
                if stack[-1] != '(':
                    stack.append(i)
                else:
                    stack.pop()

        print(stack)
                
        return len(stack)