#include <iostream>

using namespace std;

int getK(string& input) {
    int end = input.size() - 1;
    while (input[end] != '0') {
        end--;
    }
    int front = end;
    while(input[front] != '1') {
        front--;
    }
    return end-front;
}

int done(string& input) {
    for(int i = 0; i < input.size(); i++) {
        if(input[i] == '0') return 0;
    }
    return 1;
}

int main()
{
    string input;
    getline(std::cin, input);

    if(input[0] == '0') {
        cout << -1 << endl;
        return 0;
    }

    int len = input.size();

    int rounds = 0;
    while(!done(input)) {
        int K = getK(input);

        //cout << "chose K: " << K << endl;

        for(int i = len-1; i >= 0; i--) {
            if(input[i] == '1') {
                if(i+K < len) {
                    input[i+K] = '1';
                }
            }
        }

        //cout << "updated input: " << input << endl;

        rounds++;
    }

    cout << rounds << endl;


    return 0;
}