#include <bits/stdc++.h>
using namespace std;
int n, cnt;
string s;
int main() {
  cin >> n >> s;
  for (int i = 0; i < n; i++) {
    if (s[i] == '-' && cnt)
      cnt--;
    else if (s[i] == '+')
      cnt++;
  }
  cout << cnt << "\n";
}
