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