Accessing Overridden Base Class Member from Derived Class in C#

using System;
class A
{
public void Add(int x,int y)
{
Console.WriteLine("sum is {0}",(x+y));
}
}
class B:A
{
new public void Add(int x, int y)
{
Console.WriteLine("sum of 2 numbers is {0}",x+y);
}
public void OldAdd(int x,int y)
{
base.Add(x,y);
}
}
class Demo
{
public static void Main()
{
B obj=new B();
obj.Add(10,20);
obj.OldAdd(20,40);
}
}

output:

sum of 2 numbers is 30