#include <iostream>
#include <cmath>
using namespace std;

int main() {
    int n = 0, max = 0;

    char c;
    cin >> c;

    while (cin >> c) {
        if (c == '0')
            n++;
        else {
            max = ceil(n/2.) > max ? ceil(n/2.) : max;
            n = 0;
        }
    }

    cout << max << endl;
    return 0;
}