#include <iostream>
using namespace std;

int main(){
	
	char c[40] = {' '};
	cin>>c;

	int size = 0;
	for(int i=0; i<40; i++){if(c[i]=='0' || c[i]=='1') size ++;}

	//cout <<size<<endl;
//size = 9;
	int counter = 0;
	//char tmp[40];
	while(true){
		int indx=-1, indxOne = -1;
		//tmp = c;

		for(int i=0; i<size; i++){
			if(c[i] == '0' && indx == -1){
				indx = i;
			}
			if(c[i] == '1'){indxOne = i; }	
		}

		if(indx==-1 || indxOne == size-1) break;
		

		int k = indx;
		if(size - indxOne < k) k = size - indxOne;
/*
		for(int i=0; i<size; i++){
			if((i+k) < size && c[i+k] == '0'){
				tmp[i+k] = '1';
			}	
		}
*/

//cout << indxOne << " " << k<<endl;
		for(int i=size-1; i>-1; i--){

			if((i-k) > -1 && c[i-k] == '1'){
				c[i] = '1';
			}	
		}


		//cout<<c<<endl;
counter++;
		//c = tmp;

	}
	if(counter == 0){cout << -1;}
	else{cout << counter;}
	


	return 0;
}