#include <iostream>


bool all_ones(const std::string & line) {
    for (const char i : line) {
        if (i != '1' and i != '\n') {
            return false;
        }
    }
    return true;
}


int main(int, char**) {

    std::string line;
    std::getline(std::cin, line);
    size_t days = 0;

    while (not all_ones(line)) {
        auto copy = line;
        bool day_changed = false;
        for (size_t i = 0; i < line.length(); ++i) {
            if (i > 0 and line[i] == '1') {
                day_changed = day_changed or copy[i-1] == '0';
                copy[i-1] = '1';
            }
            if (i < line.length()-1  and line[i] == '1') {
                day_changed = day_changed or copy[i+1] == '0';
                copy[i+1] = '1';
            }
        }
        days += day_changed;
        line = copy;
    }

    std::cout << days << std::endl;

}