#include <bits/stdc++.h>
using namespace std;
int main(){
	int n;
	cin>>n;
	cout<<(n%10)+(n/10%10)+(n/100%10)+(n/1000);
	;return 0;
	}
/**************************************************************
	Problem: 1390
	User: ljl2
	Language: C++
	Result: Accepted
	Time:16 ms
	Memory:2072 kb
****************************************************************/