Yay recursion!

import java.io.PrintWriter;
import java.util.Scanner;

/**
 * 
 * @author Sanchit M. Bhatnagar
 * @see http://uhunt.felix-halim.net/id/74004
 * 
 */
public class P11332 {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		PrintWriter out = new PrintWriter(System.out);

		while (true) {
			long x = sc.nextLong();
			if (x == 0)
				break;
			out.println(solve(x));
		}

		out.close();
		sc.close();
	}

	private static long solve(long x) {
		if (x < 10)
			return x;

		long sum = 0;
		while (x > 0) {
			sum += x % 10;
			x /= 10;
		}

		return solve(sum);
	}

}