#include<iostream>
#include<vector>
#include<string>

using namespace std;

int main(){
	string s;

	cin >> s;

	int ones = 0;
	int zeroflag = 0;

	char arr[41];

	for(auto i = 0; i < s.size(); ++i){
		arr[i] = s[i];
	}

	int goal = 0;

	for(auto i = 0; i < s.size(); ++i){
		if(s[i] == '0' && i == 0){
			cout << "-1\n";
			return 0;
		}else if(s[i] == '0'){
			zeroflag = 1;
			for(auto j = 0; j < s.size(); ++j){
				if(arr[j] == '1'){
					int index = j + i;
					if(index < s.size()){
						s[index] = '1';
					}
				}
			}
			for(auto i = 0; i < s.size(); ++i){
				arr[i] = s[i];
			}
			++goal;
		}
	}

	cout << goal << "\n";

	return 0;
}