Crooked Digits

using System;
using System.Linq;
using System.Numerics;

namespace CroockedDigits

{
    class Program
    {
        static void Main(string[] args)
        {
            string input = Console.ReadLine();
            string clearedInput = input.Replace(".", "").Replace("-" , "");
            BigInteger parseInput = long.Parse(clearedInput);
            BigInteger n = parseInput;
            BigInteger sum = 0;

                while (n > 0 || sum > 9)
                {
                    if (n == 0)
                    {
                        n = sum;
                        sum = 0;
                    }
                    sum += n % 10;
                    n = n / 10;
                }
                Console.WriteLine(sum);
            //bie mi IR na nqkoi ot testovete
            //test s Biginteger
            //pak pishe IRA

        }
    }
}