#include <bits/stdc++.h>
using namespace std;
long double pi = 3.14159265358979323846;
vector<long long> al[500005];
long long vis[500005], color[500005], I[101][101];
long long gcd(long long a, long long b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
bool isPrime(int n) {
  if (n <= 1) return false;
  if (n <= 3) return true;
  if (n % 2 == 0 || n % 3 == 0) return false;
  for (int i = 5; i * i <= n; i = i + 6)
    if (n % i == 0 || n % (i + 2) == 0) return false;
  return true;
}
long long binpow(long long n, long long po) {
  long long res = 1;
  while (po > 0) {
    if (po % 2) {
      res *= n;
      po--;
    } else {
      n *= n;
      po /= 2;
    }
  }
  return res;
}
long long swap(long long a, long long b) {
  a = a + b;
  b = a - b;
  a = a - b;
}
long long fact(long long n) {
  if ((n == 0) || (n == 1))
    return 1;
  else
    return n * fact(n - 1);
}
long long C(long long n, long long r) {
  if (r > n - r) r = n - r;
  long long ans = 1;
  long long i;
  for (i = 1; i <= r; i++) {
    ans *= n - r + i;
    ans /= i;
    ans = ans % 1000000007;
  }
  return ans;
}
void mmul(long long A[][101], long long B[][101], long long dim) {
  long long res[dim][dim];
  for (long long i = 0; i < dim; i++)
    for (long long j = 0; j < dim; j++) {
      res[i][j] = 0;
      for (long long k = 0; k < dim; k++)
        res[i][j] = (res[i][j] + A[i][k] * B[k][j]) % 1000000007;
    }
  for (long long i = 0; i < dim; i++)
    for (long long j = 0; j < dim; j++) A[i][j] = res[i][j];
}
void mpow(long long A[][101], long long dim, long long po) {
  for (long long i = 0; i < dim; i++)
    for (long long j = 0; j < dim; j++) {
      if (i == j)
        I[i][j] = 1;
      else
        I[i][j] = 0;
    }
  while (po > 0) {
    if (po % 2 == 1) {
      mmul(I, A, dim);
      po--;
    } else {
      mmul(A, A, dim);
      po /= 2;
    }
  }
  for (long long i = 0; i < dim; i++)
    for (long long j = 0; j < dim; j++) A[i][j] = I[i][j];
}
int main() {
  long long n, o = 0, c = 0;
  cin >> n;
  string s;
  cin >> s;
  long long a[n];
  for (long long i = 0; i < n; i++) a[i] = 0;
  for (long long i = 0; i < n; i++) {
    if (s[i] == '(') {
      o++;
      if (i > 0)
        a[i] += a[i - 1] + 1;
      else
        a[i]++;
    } else {
      c++;
      if (i > 0)
        a[i] += a[i - 1] - 1;
      else
        a[i]--;
    }
  }
  long long ans = 0;
  if (o != c)
    ans = -1;
  else {
    for (long long i = 0; i < n; i++) {
      if (a[i] < 0)
        ans++;
      else if (a[i] > 0)
        continue;
      else if (a[i] == 0 && a[i - 1] < 0)
        ans++;
    }
  }
  cout << ans << "\n";
}
