using System;
using System.Collections.Generic;
using System.Text;

public class Solution {
    public string makeGood(string s) {
        // ToDo: Write Your Code Here.
        var stack = new Stack<char>();

        foreach(var c in s)
        {
            if(stack.Count > 0 && char.ToLower(stack.Peek()) == char.ToLower(c) && stack.Peek() != c)
            {
                stack.Pop();
            }
            else
            {
                stack.Push(c);
            }
        }

        var reverse = new Stack<char>();

        while (stack.Count > 0)
        {
            reverse.Push(stack.Pop());
        }

        return string.Join("", reverse);
    }
}