How To get First or second weekday of month

public static DateTime? FindMonthWeekDay( int year, int month, int offset )
{
  if ( offset < 1 || offset > DateTime.DaysInMonth( year, month ) )
  {
    throw new ArgumentOutOfRangeException( "offset" );
  }

  DateTime moment = new DateTime( year, month, 1 );
  while ( moment.Month == month )
  {
    DayOfWeek dayOfWeek = moment.DayOfWeek;
    if ( dayOfWeek != DayOfWeek.Saturday && dayOfWeek != DayOfWeek.Sunday )
    {
      offset--;
    }
    if ( offset == 0 )
    {
      return moment;
    }
    moment = moment.AddDays( 1 );
  }
  return null;
} // FindMonthWeekDay