#include <bits/stdc++.h>
using namespace std;
int main(){
	
	int i,a,b,c,d,n;
	cin>>i;
	b=i/100%10;
	a=i/1000;
	d=i%10;
	c=i/10%10;
	n=d+c+b+a;
	cout<<n;

}

/**************************************************************
	Problem: 1390
	User: huangyaojie3
	Language: C++
	Result: Accepted
	Time:18 ms
	Memory:2072 kb
****************************************************************/