using System;

public class Program

{

    public static void Main()

    {

        var ApplicationEffectiveDate = Convert.ToDateTime("2022-10-10");

        var ApplicationExpiryDate = ApplicationEffectiveDate.AddDays(15);

        var BirthDate = Convert.ToDateTime("1992-10-11");

        var CurrentBirthday = default(DateTime);

        if (IsBirthdayInRange(BirthDate, ApplicationEffectiveDate, ApplicationExpiryDate, out CurrentBirthday))

            ApplicationExpiryDate = CurrentBirthday;

        Console.WriteLine(ApplicationExpiryDate.ToString("yyyy-MM-dd"));

    }

    public static bool IsBirthdayInRange(DateTime Birthday, DateTime Start, DateTime End, out DateTime CurrentBirthday)

    {

        CurrentBirthday = Birthday.AddYears(Start.Year - Birthday.Year);

​

        if (CurrentBirthday < Start)

            CurrentBirthday = CurrentBirthday.AddYears(1);

​

        return Birthday <= End && CurrentBirthday > Start && CurrentBirthday <= End;

    }

}