using System;
using System.Linq;
using System.Collections.Generic;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Numerics;

namespace CrockedDigits2
{
    class Program
    {
        static void Main(string[] args)
        {

            string n = Console.ReadLine();
            int result = 0;

            do
            {
                result = 0;

                foreach (char item in n)
                {
                    if (Char.IsDigit(item))
                    {
                        result += (int)Char.GetNumericValue(item);
                    }
                }
                n = result.ToString();

            } while (n.Length > 1);

            Console.WriteLine(result);

        }
    }
}