#include <iostream>
using namespace std;
int main() {
    int n;
    while (cin >> n) {
        string s;
        cin >> s;
        long long cnt = 0, cur = 0, maxx = 0;
        for (char c : s) {
            if (c == '1') {
                cnt++;
                cur = max(cur - 1, -1LL);
            } else {
                cur = max(cur + 1, 1LL);
            }
            if (cur > maxx) 
				maxx = cur;
        }
        cout << cnt + maxx << "\n";
    }
    return 0;
}