#include <iostream>
using namespace std;
int n;
int h(int a){
	int b=0;
	while(a!=0){
		b=b+a%10;
		a/=10;
	}
	return b;
}
void f(int x){
	if(x<10){
		cout<<x;
	}else{
		f(h(x));
	}
}
int main(){
    cin>>n;
    f(n);
}
/**************************************************************
	Problem: 1514
	User: panyuchen
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/