#include <iostream>

int main() {
    int counter = 0;
    int max = 0;

    char i;
    while ((std::cin >> i)) {
        if (i == '1') {
            if (counter > max) max = counter;
            counter = 0;
        } else {
            ++counter;
        }
    }

    std::cout << (max + (max % 2)) / 2 << std::endl;

    return 0;
}