use strict;

while (<DATA>) {
   chomp;
   my ($numbs) = $_ =~ /^(\d+)/;
   my $formatted = sprintf("%06d",$numbs) . '.jpg';
   my ($dir) = $formatted =~ /^(\d\d\d)/;
   print "filename: $formatted\t\tdirname: $dir\n";   
}

__DATA__
123.jpg
1234.jpg
12345.jpg
123456.jpg