using System;

​

public abstract class Person

{

    public abstract string GetPostcode();

}

​

public class Customer : Person

{

    public override string GetPostcode()

    {

        return "Something";

    }

}

​

public class Program

{

    public static void Main(string[] args)

    {

        var person = new Customer();

        Console.WriteLine(person.GetPostcode());

    }

}