#include <bits/stdc++.h>

int ri() {
	int n;
	scanf("%d", &n);
	return n;
}

int main() {
	std::string s;
	std::cin >> s;
	int res = 0;
	for (int i = 1; i < (int) s.size(); i++) if (s[i] != '0') res++;
	printf("%d\n", res);
	return 0;
}