#include <iostream>
#include <vector>
using namespace std;

int vectorSumm(vector<bool> v) {
	int summ=0;
	for (int i=0; i<v.size(); i++) {
		if (v[i]) summ++;
	}
	return summ;
}

int main() {
	vector<bool> corrals;
	string inpt;
	cin >> inpt;
	
	for (int i=0; i<inpt.length(); i++) {
		corrals.push_back(((int)(inpt[i]-'0'))==1);
	}
	
	
	if (!corrals[0]) {
		cout << -1;
		return 0;
	}
	
	int best=0;
	
	while (true) {
		bool all = false;
		int cnt=0;
		
		for(size_t i = 0; i < corrals.size(); ++i){
			if(corrals[i])
			cnt ++;
			else break;
		}
		if(cnt == (int)corrals.size())
			break;
			
		++best;
		for(size_t i = corrals.size()-1; i >= cnt; --i){
			if(corrals[i - cnt]){
				corrals[i] = true;
			} 
		}
	}
	/*
	vector<bool> corralsCurr;
	vector<bool> corralsCurrCurr;
	
	int vectorSumPrev, vectorSumNow;
	vectorSumPrev = vectorSumNow = 0;
	
	int iterations;
	
	for (int K=1; K<corrals.size(); K++) {
		corralsCurr=corrals;
		iterations=0;
		vectorSumPrev=245724;
		vectorSumNow=14512345;
		while (vectorSumPrev!=vectorSumNow && vectorSumNow != corrals.size()) {
			iterations++;
			vectorSumPrev = vectorSumm(corralsCurr);
			corralsCurrCurr=corralsCurr;
			for (int j = 0; j<corralsCurr.size(); j++) {
				if (corralsCurr[j]) {
					if (j+K<corralsCurr.size()) {
						corralsCurrCurr[j+K]=true;
					}
 				}
			}
			corralsCurr=corralsCurrCurr;
			vectorSumNow= vectorSumm(corralsCurr);
		}
		if (vectorSumm(corralsCurr) == corrals.size()) {
			if (iterations<best) {
				best = iterations;
			}
		}
	}
	*/
	
	cout << best;
	
	return 0;
}