my %pad = ( 1 => 0, 4 => 3, 9 => 4, 13 => 6 );
my $longest = 6;

##</code><code>##

my $sentence = 11;

##</code><code>##

my $padded = sum map $pad{$_}, grep $sentence>=$_, keys %pad;
my $chapter    = int( $padded / $longuest ) + 1;
my $in_chapter =      $padded % $longuest   + 1