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;
	}
}

//https://pt.stackoverflow.com/q/134961/101