/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */

/* 
 * File:   clockwork.cpp
 * Author: cteam047
 *
 * Created on December 2, 2018, 9:50 AM
 */

#include <cstdlib>
#include <cstring>
#include <iostream>
#include <cmath>
using namespace std;


/*
 * 
 */
int main(int argc, char** argv) {
    string sr = "";
    cin >> sr;
    int gM = 0;
    if(sr[0] == '0'){
        cout << -1<<endl;
        return 0;
    }
    if(sr.size() == 1 && sr[0] == '1'){
      cout << 0 <<endl;
      return 0;
    }
    int array[] ={0,0};
    //array[0] = zeroes
    //array[1] = ones
    for(int i = 0; i < sr.size(); i++){
        if(sr[i] == '0'){
            array[0]++;
        }
        else{
            array[1]++;
        }
        
        if((i+1 < sr.size() && sr[i+1] == '1' && sr[i] == '0')|| (i == (sr.size() -1 ))){
            int k, M;
            if(array[0] == array[1]){
                k = array[0];
                M=1;
                if(M > gM){
                gM = M;
                }
                continue;
            }

            k = M = 0;
            while (k != 1){               
                k = array[0] / 2;
                if(array[0] % 2 != 0){
                    k++;
                }
                array[0] -= k;
                M++;                                
            }   
            k = array[0] / 2;
            if(array[0] % 2 != 0){
                k++;
            }
            array[0] -= k;
            M++;
            array[0] = array[1] = 0;
            
            if(M > gM){
                gM = M;
            }
        }
    }
    cout << gM << endl;
    return 0;
}