#include<bits/stdc++.h>
using namespace std;

int main(){
  int N;
  cin >> N;
  string S;
  cin >> S;

  vector<int>lscore(N + 1, -1e9);
  vector<int>rscore(N + 1, -1e9);
  lscore[0] = 0;
  rscore[N] = 0;
  {
    int score = 0;
    int sum = 0;
    bool exist = false;
    for(int i = 0; i < N; i++){
      if(S[i] != '(' && sum <= 1){
        lscore[i + 1] = score + exist;
      }
      if(S[i] == ')' || (S[i] == '?' && (exist || i == N - 1 || S[i + 1] == '('))){
        if(sum == 0){
          score += exist;
          exist = false;
        }
        else{
          exist = true;
          sum--;
        }
      }
      else{
        sum++;
        exist = true;
      }
    }
  }

  {
    int score = 0;
    int sum = 0;
    bool exist = false;
    for(int i = N - 1; i >= 0; i--){
      if(S[i] != ')' && sum == 0){
        rscore[i] = score + exist;
      }
      if(S[i] == '(' || (S[i] == '?' && (exist || i == 0 || S[i - 1] == ')'))){
        if(sum == 0){
          score += exist;
          exist = false;

        }
        else{
          exist = true;
          sum--;
        }
      }
      else{
        sum++;
        exist = true;
      }
    }
  }

  int ans = 0;
  for(int i = 0; i <= N; i++){
    ans = max(ans, lscore[i] + rscore[i]);
  }
  cout << ans << endl;
}