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

int main(){
	string s;
	long long h=0;
	getline(cin,s);
	for(int i=0;i<s.size();i++){
		if(s[i]=='1') h++;
	}
	cout<<h;
	return 0;
}
/**************************************************************
	Problem: 1934
	User: linzihang
	Language: C++
	Result: Accepted
	Time:70 ms
	Memory:2076 kb
****************************************************************/