open(INPUT, '< your-input-file.txt') or die "Badness: $!";
my (@instructors_array, %instructors_hash);
while (<INPUT>) {
  my ($id, $name, $class, $instructor) = split(/!/);
  push @instructors_array, $instructor;
  $instructors_hash{$instructor}++;
}
close(INPUT);
my @array_with_every_entry_sorted = sort @instructors_array;
my @array_with_distinct_entries = sort keys %instructors_hash;