use List::MoreUtils qw/last_index/;
my @vacation_skip = (7, 15, 20, 21, 22, 23, 25, 31);
my $search_for    = 18;
my $found         = last_index { $_ <= $search_for } @vacation_skip;
if ($found % 2 == 0) {
    print "vacation\n";
} else {
    print "work day\n";
}