using System;

​

public class Program

{

    static void Main()

    {

    }

​

    /// <summary>

    /// Given a non-negative integer, repeatedly add all its digits until the result has only one digit

    ///

    /// EXAMPLES:

    ///

    /// Input: 38 --> Output: 2 (3 + 8 = 11, 1 + 1 = 2)

    /// Input: 1337 --> Output 5 (1 + 3 + 3 + 7 = 14, 1 + 4 = 5)

    ///

    /// </summary>

    /// <param name = "num">The number</param>

    /// <returns>The sum of its digits until the result has only one digit</returns>

    static int AddDigits(int num)

    {

        return 0;

    }

}