/* FILE: editFormulaDP.cpp   last change: 1-Jul-2013   author: Romeo Rizzi
 * a solver for problem editFormula based on dynamic programming
 */

#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;

const int MAX_N = 500;  // massima cardinalita' della stringa in input
char s[MAX_N]; // la stringa in input
int n;  // lunghezza della stringa in input

int opt[MAX_N +1][MAX_N +1];   /* opt[i][j] = the minimum cost of a sequence of operations that fixes the interval string s[i..j) where the character in position j is the first excluded. Here i <= j and s[i,i) is the empty string. */

int main() {
  ifstream fin("input.txt"); assert( fin );
  fin >> n;
  for(int i = 0; i < n; i++)  fin >> s[i];
  fin.close();
  for(int i = n-1; i >= 0; i--)
    for(int j = i; j <= n; j++)
        if( i >= j ) opt[i][j] = 0;
        else {
          opt[i][j] = 1 + opt[i+1][j]; // DELETION del carattere in posizione i
          for(int h = i+1; h < j; h++) // the character in position i is mated with the character in position h 
	    opt[i][j] = min(
                            opt[i][j],
                            opt[i+1][h] + opt[h+1][j]
			      + ( (s[i] != '(') ? 1 : 0 ) 
			      + ( (s[h] != ')') ? 1 : 0 ) 
                           );
	  // cout << "opt[" << i << "," << j << "] = " << opt[i][j] << endl;
        }
  ofstream fout("output.txt");
  fout << opt[0][n] << endl;
  fout.close();
  return 0;
}