#include <bits/stdc++.h>
//#include "atcoder/fenwicktree"
using namespace std;
typedef long long ll;
const int INF = 1<<30;
const ll INFLL = 1LL<<60;
const ll MOD = 998244353;
const double INFD = 1.0E18;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, -1, 0, 1};
//const int dx[8] = {1, 1, 0, -1, -1, -1, 0, 1};
//const int dy[8] = {0, 1, 1, 1, 0, -1, -1, -1};
using Pair = pair<ll, ll>;
using Graph = vector<vector<pair<int, int>>>;



int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(15);
    int n; cin >> n;
    string s; cin >> s;
    int r, m; cin >> r >> m; //r==0, m==1
    int cnt = 0;
    if (n % 2){
        cout << -1 << endl;
        return 0;
    }
    for (int i = 0; i < n; i++){
        if (s[i] == '(') cnt++;
    }
    
    cout << max(n - cnt, cnt) - n / 2 << endl;
    
    return 0;
}