Stack Problem

#include <iostream>
#include <bits/stdc++.h>
using namespace std;

int main() {
    stack <char> stk;
    string a;
    cin >> a;

    if(a[0] == '(') {
        for (int i = 0; i < a.length(); i++) {
            if (a[i] == '(') {
                stk.push(a[i]);
            } else if (a[i] == ')') {
                stk.pop();
            }
        }
    } else if(a[0] == ')') {
        return false;
    }



    if(stk.size() == 0) {
        cout << "Valid" << endl;
    } else {
        cout << "Invalid" << endl;
    }

    return 0;
}