#include <bits/stdc++.h>
using namespace std;
#define modulo 1000000007
#define mod(mod_x) ((((long long)mod_x+modulo))%modulo)
#define Inf 1000000000000000010



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