#include <bits/stdc++.h>
#define PI 3.14159265359
using namespace std;

int main() {
	string C;
	cin >> C;
	//cout << stoi("01") << endl;
	//cout << to_string(1) << endl;

	cout << C.size() - 1 - count(C.begin(), C.end(), '0') << endl;
}