#include<bits/stdc++.h>
using namespace std;
int he(int x){
	int sum=0;
	while(x>0){
		//789%10=9
		sum+=x%10;
		x=x/10;
	}
	return sum;	 
}
void f(int x){
	if(x<10) {
		cout<<x;
		return;
	}
	else{
		f(he(x));	
	}	
	//压缩 
}

int main(){
	int n;
	cin>>n;
	f(n); 


	return 0;
}



/**************************************************************
	Problem: 1514
	User: admin
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/