using System;
 
class A {
  public int x = 0;
  public void f () { Console.WriteLine ( "A:f" ); } }
 
class B : A {
  public int x = 1;
  public void f () { Console.WriteLine ( "B:f" ); } }
 
public class Program {
  public static void Main ( String [] args ) {
    A a = new A ();
    B b = new B ();
    A ab = new B ();
 
    a.f();
    b.f();
    ab.f();
    Console.WriteLine ( a.x );
    Console.WriteLine ( b.x );
    Console.WriteLine ( ab.x ); } }