/* -*- coding: utf-8 -*-
 *
 * 3144.cc:  No.3144 Parentheses Modification and Rotation (01 Ver.) - yukicoder
 */

#include<cstdio>
#include<algorithm>

using namespace std;

/* constant */

const int MAX_N = 100000;

/* typedef */

/* global variables */

char s[MAX_N + 4];

/* subroutines */

/* main */

int main() {
  int n, r, m;
  scanf("%d%s%d%d", &n, s, &r, &m);
  if (n & 1) { puts("-1"); return 0; }
  
  int c0 = 0;
  for (int i = 0; i < n; i++)
    if (s[i] == '(') c0++;
  int c1 = n - c0;

  printf("%d\n", abs(c1 - c0) / 2);
  
  return 0;
}