using System;

public class Program

{

    public static void Main()

    {

        var a = new A();

        var b = new B();

        var c = new C();

        var d = new D();

        var e = new E();

        Console.WriteLine(GetClassName(a));

        Console.WriteLine(GetClassName(b));

        Console.WriteLine(GetClassName(c));

        Console.WriteLine(GetClassName(d));

        Console.WriteLine(GetClassName(e));

    }

    public static string GetClassName<T>(T item) where T : A {

        return item.GetClassName();

    }

    public static string GetClassName(D item) {

        return item.GetClassName();

    }

    public class A     { public virtual string GetClassName() => "A"; }

    public class B : A { public override string GetClassName() => "B"; }

    public class C : A { public override string GetClassName() => "C"; }

    public class D     { public virtual string GetClassName() => "D"; }

    public class E : C { public override string GetClassName() =>  "E"; }

}