using System;

public class Program {

    public static void Main() {

        Console.WriteLine((new DateTime(2016, 06, 13)).BusinessDaysUntil(DateTime.Now));

    }

}

public static class DateExt {

    public static int BusinessDaysUntil(this DateTime firstDay, DateTime lastDay, params DateTime[] bankHolidays) {

        firstDay = firstDay.Date;

        lastDay = lastDay.Date;

        if (firstDay > lastDay)

            throw new ArgumentException("Incorrect last day " + lastDay);

        TimeSpan span = lastDay - firstDay;

        int businessDays = span.Days + 1;

        int fullWeekCount = businessDays / 7;

        // find out if there are weekends during the time exceedng the full weeks

        if (businessDays > fullWeekCount*7) {

            // we are here to find out if there is a 1-day or 2-days weekend

            // in the time interval remaining after subtracting the complete weeks

            int firstDayOfWeek = (int) firstDay.DayOfWeek;

            int lastDayOfWeek = (int) lastDay.DayOfWeek;

            if (lastDayOfWeek < firstDayOfWeek)

                lastDayOfWeek += 7;

            if (firstDayOfWeek <= 6)

            {

                if (lastDayOfWeek >= 7)// Both Saturday and Sunday are in the remaining time interval

                    businessDays -= 2;

                else if (lastDayOfWeek >= 6)// Only Saturday is in the remaining time interval

                    businessDays -= 1;

            }

            else if (firstDayOfWeek <= 7 && lastDayOfWeek >= 7)// Only Sunday is in the remaining time interval

                businessDays -= 1;

        }

        // subtract the weekends during the full weeks in the interval

        businessDays -= fullWeekCount + fullWeekCount;

        // subtract the number of bank holidays during the time interval

        foreach (DateTime bankHoliday in bankHolidays) {

            DateTime bh = bankHoliday.Date;

            if (firstDay <= bh && bh <= lastDay)

                --businessDays;

        }

        return businessDays;

    }

}