using System;

​

public class Program

{

    public static void Main()

    {

        DoCS();

    }

​

    public static void DoCS()

    {

        var start = new DateTime(2019, 11, 13, 0, 0, 0, DateTimeKind.Utc);

        var end = new DateTime(2020, 12, 13, 0, 0, 0, DateTimeKind.Utc);

        var durationDays = DateUtils.InclusiveDifferenceInDaysBetween(start, end);

        var durationWeeks = (decimal)durationDays / 7;

        var holidayDays = (int)Math.Ceiling(durationDays * (28 / 365M));

        var holidayWeeks = (decimal)holidayDays / 5;

        var durationInWeeks = (int)Math.Ceiling(durationWeeks - holidayWeeks);

        var totalWorkingMinutesPerWeek = (39 * 60);

        var result = (int)Math.Ceiling(durationInWeeks * totalWorkingMinutesPerWeek / 60M * 0.2M);

        Console.WriteLine($"Off The JobHours CS - {result}");

    }

}

​

public class DateUtils

{

    public static int InclusiveDifferenceInDaysBetween(DateTime date1, DateTime date2) => (int)Math.Abs((date1 - date2).TotalDays) + 1;

    public static int InclusiveDifferenceInWeeksBetween(DateTime date1, DateTime date2, int excludeDays = 0)

    {

        var days = InclusiveDifferenceInDaysBetween(date1, date2) - Math.Abs(excludeDays);

        return (int)Math.Ceiling((decimal)days / 7);

    }

}