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

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

    int max_sum = 0;
    int current = 0;

    for (char c : S) {
        int val = (c == '0' ? 1 : -1);
        current = max(val, current + val);
        max_sum = max(max_sum, current);
    }

    cout << max_sum << '\n';
    return 0;
}