#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<cmath>
#include<algorithm>
using namespace std;
int main(){
	// freopen("numbergame.in","r",stdin);
	// freopen("numbergame.out","w",stdout);
    string s;
    cin >> s;
    int res=0;
    for(int i=0;i<s.length();i++){
    	if(s[i]=='1'){
    		res++;
    	}
    }
    cout << res;
	// fclose(stdin);
	// fclose(stdout);
	return 0;
}

#include <iostream>
#include <string>
using namespace std;
int main()
{
	string s;
	cin>>s;
	int sum = 0;
	for (int i = 0;i <= s.size()-1;i++)
		if(s[i] == '1')sum += 1;
	cout<<sum<<endl;
	return 0;
}