#!/usr/bin/perl

use strict;
use warnings;

use Data::Dumper;

my $data = join '', map {chomp; $_} (<DATA>);
my @data;
my @results;

do { 
    push @data, substr $data,0,5; substr $data,0,1,'' 
} while ( length $data > 4);

while (@data) {
    my $cur = shift @data;
    my $p   = 1;
       $p  *= $_ for split //, $cur; 

    push @results, [$cur, $p];
}

my $max = [0,0];
for (@results) { $max = $_ if $_->[1] > $max->[1] };
print Dumper $max;

__DATA__
73167176531330624919225119674426574742355349194934
96983520312774506326239578318016984801869478851843
85861560789112949495459501737958331952853208805511
12540698747158523863050715693290963295227443043557
66896648950445244523161731856403098711121722383113
62229893423380308135336276614282806444486645238749
30358907296290491560440772390713810515859307960866
70172427121883998797908792274921901699720888093776
65727333001053367881220235421809751254540594752243
52584907711670556013604839586446706324415722155397
53697817977846174064955149290862569321978468622482
83972241375657056057490261407972968652414535100474
82166370484403199890008895243450658541227588666881
16427171479924442928230863465674813919123162824586
17866458359124566529476545682848912883142607690042
24219022671055626321111109370544217506941658960408
07198403850962455444362981230987879927244284909188
84580156166097919133875499200524063689912560717606
05886116467109405077541002256983155200055935729725
71636269561882670428252483600823257530420752963450

    my $max = 0;
    while ( $digits ) {                         # iterate through $digits
        my $next = substr( $digits, 0, $nod );  # get next digits
        
        my @fac  = split( '', $next );          # get factors
        my $cur  = 1;
           $cur *= $_ for ( @fac );             # multiply
        $cur > $max and $max = $cur;            # set as maximum if needed
        
        substr( $digits, 0, 1, '' );            # delete 1st digit
    } # while