using System;

public class Program

{

    public static void Main()

    {

        int x = DigitalRoot(83);

        Console.WriteLine(x);

    }

    public static int DigitalRoot(int num){

        int result = 0;

        string numstr = num.ToString();

        int curr;

        bool cn = true;

        while (cn){

            for (int x = 0; x < numstr.Length; x++){

                curr = Int32.Parse(numstr.Substring(x, 1));

                result = result + curr;

            }

            if (result < 10){

                cn = false;

            }

            numstr = result.ToString();

        }

        return result;

    }

}