Run time polymorphism using c#

Program to implement Run-time polymorphism using virtual function concept

using System;
using System.Collections.Generic;
using System.Text;

namespace ConsoleApplication32
{
class a
{
public int s, r;
public virtual void add()
{
s = 23;
r = 56;
Console.WriteLine(s);
Console.WriteLine(r );

Console.WriteLine("base class a");
}
}
class b:a
{

public override void add()
{
s = 389;
r = 7648;
Console.WriteLine(s);
Console.WriteLine(r);

Console.WriteLine("derived class b");
}

}
class c:a
{

static void Main(string[] args)
{
b b1 = new b();
b1.add();
c c1 = new c();
a a1 = new a();

}
}
}