sub getThirdFriday(){
  my ($year, $month)=@_;
  my $startThirdWeek=15;
  my $dow = Day_of_Week($year, $month, "15");
  if ($dow<6) {
    return $startThirdWeek+5-$dow;
  }
  else {
    return $startThirdWeek+12-$dow;
  }