#include<iostream>
using namespace std ;
int main() {
	int j;
	cin>>j;
	int k = j / 1000;
	int l = j % 1000 / 100;
	int m = j % 100 / 10;
	int n = j % 10;
	int o = k + l + m + n;
	cout<< o <<endl; 
}