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