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

namespace DemoTest
{
    class Program
    {
        static void Main(string[] args)
        {
            B a = new B();
        }
    }
    public class A
    {
        public A()
        {
            Say();
        }
        protected virtual void Say() {
            Console.WriteLine("A");
        }
    }

    public class B : A
    {
        protected override void Say()
        {
            Console.Write("B");
        }
    }
}