#include <vector>
#include <string>
#include <iostream>
#include <cmath>

using namespace std;

int main() {
    string s;
    cin >> s;

    vector<int> v;
    int c = 0;
    for (int i = 0; i < s.size(); i++) {
        if (s[i] == '1') {
            v.push_back(c);
            c = 0;
        } else {
            c++;
        }
    }

    int m = 0;
    for (int i = 0; i < v.size(); i++) {
        if (v[i] > m) {
            m = v[i];
        }
    }
    cout << ceil(m / 2.0) << endl;

    return 0;
}