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

#define rep(i, a, b) for (int i = a; i < b; i++)
using ll = long long;

int main() {
	int n;
	string s;
	cin >> n >> s;
	vector<int> a(n), d;
	int m = -1e9, p = 1;
	rep(i, 0, n) {
		if(s[i] == '0') continue;
		else {
			if(s[i] == '+') a[i] = p++;
			else a[i] = m++;
		}
	}
	rep(i, 0, n) {
		int j = lower_bound(d.begin(), d.end(), a[i]) - d.begin();
		int sz = d.size();
		if(j == sz) d.push_back(a[i]);
		else d[j] = a[i];
	}
	cout << d.size() << endl;
}