class Solution(object):
    def makeGood(self, s):
        """
        :type s: str
        :rtype: str
        """
        stack=[]
        for i in s:
            if len(stack)==0:
                stack.append(i)
            else :
                if ord(i)-32==ord(stack[-1]) or ord(i)==ord(stack[-1])-32:
                    stack.pop()
                else:
                    stack.append(i)   
        s=''
        for i in stack:
            s+=i
        return s