use strict;
use warnings;

my $info = {};
while (my $line = <>) {
  my ($row_id, $book_id, $chapter, $section) = split /\t/, $line;
  
  if (defined $info->{$book_id}{$chapter}{$section}) {
    die "$book_id, $chapter, $section, line $.";
  }
  else {
    $info->{$book_id}{$chapter}{$section}++;
  }
}