#include<bits/stdc++.h>
using namespace std;
int n=0,m;
string s;
int main(){
	cin>>s;
	for(int i=0;i<=7;i++){
		
		if(s[i]=='1'){
			n++;
		}
	}
	cout<<n;
}
/**************************************************************
	Problem: 1934
	User: zhengzihao
	Language: C++
	Result: Accepted
	Time:67 ms
	Memory:2076 kb
****************************************************************/