static void Main(string[] args)
{
C c = new C();
I1 i1 = (I1)c;
I2 i2 = (I2)c;
i1.A();
i2.A();
c.A();
Console.ReadLine();
D d = new D();
i1 = (I1)d;
i2 = (I2)d;
i1.A();
i2.A();
d.A();
Console.ReadLine();
E e = new E();
i1 = (I1)e;
i2 = (I2)e;
i1.A();
i2.A();
e.A();
Console.ReadLine();
F f = new F();
//f.A(); --- COMPILE ERROR
i1 = (I1)f;
//i2 = (I2)f; --- RUNTIME ERROR
i1.A();
Console.ReadLine();
}