#include<bits/stdc++.h> 
using namespace std;
int main()
{
	int n,d; 
	cin>>n;
	d=n/1000+(n%1000)/100+(n%1000%100)/10+(n%1000%100%10);
	cout<<d<<endl;
	return 0;
}
/**************************************************************
	Problem: 1390
	User: zhangchenyu
	Language: C++
	Result: Accepted
	Time:15 ms
	Memory:2072 kb
****************************************************************/