use strict;
use warnings;
use Data::Dumper;

my @array = (1..5, 8..10, 15..30, 35..40);
my @bucket;

my $j = 0;
for my $k (0 .. $#array) {
    if ($array[$k] == $array[$k+1] - 1) {
        push @{ $bucket[$j] }, $array[$k];
    }
    else {
        $j++;
    }
}

my @ip = (sort { $#$b <=> $#$a } @bucket)[0];
print Dumper \@ip;