using System;

public abstract class Program

{

    public abstract int CalculateArea(int a, int b);

    //{

        //return a * b;

    //}

    public static void Main()

    {

        //Console.WriteLine("Hello World");

    }

}

​

public class Rectangle:Program

{

​

    Program.CalculateArea(int a, int b)

    {

    return a * b;

    }

}

​

public class Square

{

    public int CalculateArea(int a, int b)

    {

        return a * b;

    }

}