using System;

public class Program

{

    public static void Main()

    {

        var n = 172469;

        do

        {

            var sum = 0;

            while (n != 0) {

                sum += n % 10;

                n /= 10;

            }

            n = sum;

        } while (n > 10);

        Console.WriteLine(n);

    }

}