static void Main(string[] args)
{
MyClass1 A = new MyClass1(5);
MyInterface B = A;
Console.WriteLine(A.Num());
Console.WriteLine(B.Num());
MyClass2 C = new MyClass2(5);
MyInterface D = C;
Console.WriteLine(C.Num());
Console.WriteLine(D.Num());
Console.ReadKey();
}