using System;

​

abstract class Shape

{

    public abstract void area(); //abstract method, no body

    public void print() //regular method

    {

        Console.WriteLine("This is a shape.");

    }

}

​

//child class

class Square : Shape

{

    public override void area()

    {

        //overriding the abstract method

        Console.WriteLine("This is an area.");

    }

}

​

public class Program

{

    public static void Main()

    {

        Shape square1 = new Square();

        square1.print();

        square1.area();

    }

}