use strict;

sub subseqs {
   my $str = $_[0];
   my @seqs = ('');
   for my $char (split //, $str) {
       for my $i ( 0..@seqs-1 ) {
	       push @seqs, $seqs[$i].$char;
	   }
   }
   return @seqs;
}

my $s1 = 'abcdefgh';
my $s2 = 'abecdgh';
my $best_len = 0;
my $longest;
for my $seq1 (subseqs($s1)) {
    for my $seq2 (subseqs($s2)) {
	    next unless $seq1 eq $seq2;
		if (length($seq1) > $best_len) {
		    $longest = $seq1;
			$best_len = length($seq1);
		} 
	}
}
print $longest;