How to get weekno.s based on the particular date?

public static int GetWeekNumber(DateTime dtPassed)
{
        CultureInfo ciCurr = CultureInfo.CurrentCulture;
        int weekNum = ciCurr.Calendar.GetWeekOfYear(dtPassed, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);
        return weekNum;
}