class Solution {
    public int minAddToMakeValid(String s) {
    int open =0, mismatch=0;
    for(int i=0; i<s.length(); i++)
    {
     if(s.charAt(i)=='(')
     open++;
     else
     {
        if(open>0)
        open--;
        else
        mismatch++;
     }
    } 
     return open+mismatch;   
    }
}