using System;

​

    public class MyNumber

    {

        protected readonly long _value;

        public MyNumber(string source)

        {

            if (!long.TryParse(source, out _value)) throw new ArgumentException("String cannot be converted to a MyNumber");

            if (_value <=0) throw new ArgumentException("MyNumber must be at least 1.");

            if (_value > 9999999999) throw new ArgumentException("MyNumber must be ten digits or fewer.");

        }

        static public implicit operator long(MyNumber source)

        {

            return source.Value;

        }

        static public implicit operator MyNumber(string source)

        {

            return new MyNumber(source);

        }

        public long Value { get { return _value; } }

        public override string ToString()

        {

            return _value.ToString("000 000 0000");

        }

    }

    public class Program

    {

        public static void Main()

        {

            MyNumber n = "12345678";

            Console.WriteLine("Your magic number is {0}", n);

            Console.WriteLine("Another number is {0}", (MyNumber)"9876543");

        }

    }