my @ans = 
    grep {$_}
map {
    my $func = $_; 
    reduce( sub{
	my($first, $second) = @_;
	return ($first eq $second) && $first;
	}
	    , map(&$func, @data));
}
map {
    my $ctr = $_; 
    sub
    {
	my $str = $_;
	substr($str, 0, $ctr);
    }
}
(1..length($data[0]));

print pop(@ans), "\n";