using System;

public class Program

{

    public static void Main()

    {

        string n = Console.ReadLine();

        int sum = 0;

​

        while (true)

        {

            for (int i = 0; i < n.Length; i++)

            {

                if (n[i] == '-' || n[i] == '.')

                {

                    continue;

                }

                sum = sum + int.Parse(n[i].ToString());

            }

            if (sum < 10)

            {

                break;

            }

            n = sum.ToString();

            sum = 0;

        }

        Console.WriteLine(sum);

    }

}