using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

    }

}

​

public interface ITimePeriodExtractable

{

    TimePeriod ExtractTimePeriod();

}

​

public class TimePeriod

{

    public TimePeriod(DateTime startDate, DateTime endDate)

    {

        StartDate = startDate;

        EndDate = endDate;

    }

    DateTime StartDate {get; set;}

    DateTime EndDate {get; set;}

}

​

public class BillingPeriod : ITimePeriodExtractable

{

    public DateTime StartDate {get;}

    public DateTime EndDate {get; }

    public int BillingFrequency {get;}

    public TimePeriod ExtractTimePeriod()

    {

        return new TimePeriod(this.StartDate, this.EndDate);

    }

}

​

public class MemberPlan : ITimePeriodExtractable

{

    public int MemberId {get; set;}

    public DateTime StartDate {get;}

    public DateTime EndDate {get; }

    public TimePeriod ExtractTimePeriod()

    {

        return new TimePeriod(this.StartDate, this.EndDate);

    }

}

​