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

int main() {
	string c; cin >> c;
	int n = c.size();
	int ans = 0;
	for(int i = 1; i < n; ++i) {
		if(c[i] != '0') {
			++ans;
		}
	}
	cout << ans << '\n';
	return 0;
}