#include <bits/stdc++.h>
using ll = long long int;
using namespace std;
int main() {
  int n;
  cin >> n;
  string s;
  cin >> s;
  int cnt = 0;
  int negative = -1;
  int ans = 0;
  for (int i = 0; i < n; ++i) {
    if (s[i] == ')')
      --cnt;
    else if (s[i] == '(')
      ++cnt;
    if (cnt < 0 && negative == -1) negative = i;
    if (cnt == 0 && negative != -1) {
      ans += i - negative + 1;
      negative = -1;
    }
  }
  if (cnt != 0) {
    cout << -1 << endl;
  } else {
    cout << ans << endl;
  }
}
