/* FILE: editFormula.cpp   last change: 1-Jul-2013   author: Romeo Rizzi
 * a linear greedy solver for problem editFormula
 */

#define NDEBUG   // NDEBUG definita nella versione che consegno
#include <cassert>
#ifndef NDEBUG
#  include <iostream>  // uso di cin e cout non consentito in versione finale
#endif
#include <fstream>

using namespace std;

int half_rounded_up(int n) { return n/2 + (n%2); } 

int main() {
  int n;  // lunghezza della stringa in input
  char s; // carattere corrente della stringa in input
  int num_unmatched_open = 0, num_unmatched_closed = 0;

  ifstream fin("input.txt"); assert( fin );
  fin >> n;

  for(int i = 0; i < n; i++) {
    fin >> s;
    if( s == '(' ) //  s[i] == '('
      num_unmatched_open++;
    else { //  s[i] == ')' 
      if(num_unmatched_open > 0)
        num_unmatched_open--;
      else num_unmatched_closed++;
    }
  }
  fin.close();

  ofstream fout("output.txt");
  fout << half_rounded_up(num_unmatched_closed)
          + half_rounded_up(num_unmatched_open) << endl;
  fout.close();
  return 0;
}