自己看

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
ll ans=0;
string s;
int main(){
	//freopen(".in","r",stdin);
	//freopen(".out","w",stdout);
	std::ios::sync_with_stdio(false);
	std::cin.tie(nullptr);
	std::cout.tie(nullptr);
	cin>>s;
    s=" "+s;
    ll len=s.size();
    for(ll i=1;i<=len;i++){
        if(s[i]=='1'){
            ans++;
        }
    }
    cout<<ans<<endl;
	//fclose(stdin);
	//fclose(stdout);
	return 0;
}
//coder::by::M91