Get week number from a given date

public static int GetWeekNumber(string date)
{
DateTimeFormatInfo dfi = DateTimeFormatInfo.CurrentInfo;
DateTime dt = DateTime.ParseExact(date,"dd-MM-yyyy",null);
System.Globalization.Calendar cal = dfi.Calendar;
return cal.GetWeekOfYear(dt, dfi.CalendarWeekRule, dfi.FirstDayOfWeek);
}