using System;

using System.Globalization;

public class Program

{

    public static void Main()

    {

        DateTimeFormatInfo dfi = DateTimeFormatInfo.CurrentInfo;

        Calendar cal = dfi.Calendar;

        int startWeek = cal.GetWeekOfYear(new DateTime(2015, 3, 1), dfi.CalendarWeekRule, DayOfWeek.Monday);

        int endWeek = cal.GetWeekOfYear(new DateTime(2015, 3, 31), dfi.CalendarWeekRule, DayOfWeek.Monday);

        int numberOfWeeks = 1 + endWeek - startWeek; // == 6

        Console.WriteLine(numberOfWeeks);

    }

}