#include <iostream>

using namespace std;

int getK(string& input) {
    int startIndex;
    int endIndex;
    int maxZeros = 0;

    int start;
    int end;
    int zeroes = 0;
    for(int i = 0; i < input.size(); i++) {
        if(input[i] == '0') {
            if(zeroes == 0) start = i;
            zeroes++;

            if(i == input.size() - 1) {
                end = i;
                if(zeroes > maxZeros) {
                    maxZeros = zeroes;
                    endIndex = end;
                    startIndex = start;
                }
            }
        } else {
            if(zeroes != 0) {
                end = i-1;
                if(zeroes > maxZeros) {
                    maxZeros = zeroes;
                    endIndex = end;
                    startIndex = start;
                }
            }
            zeroes = 0;
        }
    }

    //cout << startIndex << " " << endIndex << " " << maxZeros << endl;

    int oneCount = 0;
    for(int i = startIndex - 1; i >= 0; i--) {
        if(input[i] == '1') {
            oneCount++;
        } else {
        break;
        }
    }



    return (maxZeros + oneCount) / 2;
}

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;
}