#include<bits/stdc++.h>
using namespace std;
int j(long long m){
	int h=0;
	while(m!=0){
		h+=m%10;
		m=m/10;
	}
	return h;
}
int main(){
	long long n;
	cin>>n;
	do{
		n=j(n);
	}while(n>10);
	cout<<n;
}
/**************************************************************
	Problem: 1514
	User: wangyiyang
	Language: C++
	Result: Accepted
	Time:7 ms
	Memory:2072 kb
****************************************************************/