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

using ll = long long;

int main()
{
    int N;
    cin >> N;

    assert(1 <= N && N <= 100000);

    string S;
    cin >> S;

    assert(S.size() == N);

    if (N % 2 == 1)
    {
        cout << "-1" << "\n";
        return 0;
    }

    int open = 0;
    int close = 0;
    for (int i = 0; i < S.size(); i++)
    {
        assert(S[i] == '(' || S[i] == ')');
        if (S[i] == '(') open++;
        else if (S[i] == ')') close++;
    }

    int ans = abs(open - close) / 2;

    cout << ans << endl;
}