using System;

public interface I
{
    void test();
}
    
public class A : I
{
    public virtual void test() { System.Console.Out.WriteLine("A\n"); }
}
    
public class B : A
{
    public override void test() { System.Console.Out.WriteLine("B\n"); }
}  
    
public class Main_
{
    public static void Main(string[] args)
    {
        Main_.doTest(new B());
    }
    public static void doTest(I i)
    {
        i.test();
    }
}