import java.util.*;
public class Main{
	public static int getS(int n){
		int i,t=n;
		while(t>=10){
			i=0;
			n=t;
			while(n>0){
				i+=n%10;
				n/=10;
			}
			t=i;
		}
		return t;	
	}



	public static void main(String args[]){
		Scanner sc=new Scanner(System.in);
		int n=sc.nextInt();
		System.out.print(getS(n));
	}
}
/**************************************************************
	Problem: 1514
	User: admin
	Language: Java
	Result: Accepted
	Time:939 ms
	Memory:39840 kb
****************************************************************/