Min Add to Make Parentheses Valid

import java.util.*;

class Solution {
    public int minParentheses(String s) {
        Stack<Character> st = new Stack<>();
        int count = 0;
        for (char ch : s.toCharArray()) {
            if (ch == '(')
                st.push(ch);
            else {
                if (!st.isEmpty())
                    st.pop();
                else
                    count++;
            }
        }
        return st.isEmpty() ? count : count + st.size();
    }
}