#include <bits/stdc++.h>
using namespace std;
#define all(p) p.begin(), p.end()
#define rep(i, a, b) for (int i = (int)(a); i < (int)(b); i++)


int main(){
    int N;
    cin >> N;
    string S;
    cin >> S;
    int R, M;
    cin >> R >> M;
    if (N % 2){
        cout << "-1\n";
    }
    else{
        int tmp = 0;
        for (auto c : S) tmp += (c == '(' ? -1 : 1);
        cout << abs(tmp) / 2 << "\n";
    }
}