using System;

class A
{
    public virtual void Foo(int x = 1)
    {
        Console.WriteLine("A.Foo({0})", x);
    }
}

class B : A
{
    public override void Foo(int x = 2)
    {
        Console.WriteLine("B.Foo({0})", x);
    }

    static void Main()
    {
        B b = new B();
        b.Foo();

        A a = b;
        a.Foo();
    }
}