#include <iostream>
#include <string>

int main() {
    std::string str;
    std::cin >> str;
    int n = str.size();
    int r = 0;
    while (true) {
        int i = 0;
        while (i < n && str[i] == '1') i++;
        if (i == 0) {
            r = -1;
            break;
        }
        if (i == n) break;
        for (int j = n - 1; j >= i; j--) {
            if (str[j-i] == '1') str[j] = '1';
        }
        r++;
    }
    std::cout << r << std::endl;
    return 0;
}