using System;

​

public enum CountryCode

{

    Undefined = default,

    DK = 10,

    PL = 20

}

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine(Enum.Parse<CountryCode>("DK"));

        Console.WriteLine(Enum.Parse<CountryCode>("10"));

        Console.WriteLine(Enum.IsDefined(Enum.Parse<CountryCode>("10")));

    }

}