import java.util.*;
import java.io.*;
public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		PrintWriter ou = new PrintWriter(System.out);
		int n = Integer.parseInt(sc.next());
		for(int i = 0 ; i < 100 ; i++){
			int s = 0 , cl = n;
			while(cl != 0){
				s += cl % 10;
				cl /= 10;
			}
			n = s;
		}
		ou.println(n);
		ou.flush();
		sc.close();
	}
}