#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using ll = long long;

int op(int lhs, int rhs){return min(lhs, rhs);}
constexpr int e(){return 1 << 30;}

int main(){
int n, r, m;
string s;
cin >> n >> s >> r >> m;
if(n % 2 == 1){
cout << "-1\n";
return 0;
}
s += s;
vector<int> sv(2 * n + 1);
for(int i = 0; i < 2 * n; i++){
sv[i + 1] = sv[i] + (s[i] == '(' ? 1 : -1);
}
atcoder::segtree<int, op, e> seg(sv);
int ans = 1 << 30;
for(int i = 0; i < n; i++){
	int mn = min(0, seg.prod(i, i + n) - sv[i]);
	int tot = (-mn + 1) / 2;
	int d = (sv[i + n] + 2 * tot) - sv[i];
	ans = min(ans, d / 2 + tot);
}
cout << ans << '\n';
}