while ( my $line = <DATA> ) {
	chomp $line;

	# remove the spaces from start of line
	if ( ! ( $line =~ s/^\s+// ) ) {
		print "\n" if $. != 1;
	}

	# remove spaces from end of line
	$line =~ s/\s+$//;
	print $line;
}

__DATA__
firstline54324563213612531436436463246324634
         secondlidfndsfdsfdsfd
         thirdlinedsfsdf   
firstline54324563213612531436436463246324634
         secondlidfndsfdsfdsfd
         thirdlinedsfsdf   

##</code><code>##

$ perl guess.pl
firstline54324563213612531436436463246324634secondlidfndsfdsfdsfdthirdlinedsfsdf
firstline54324563213612531436436463246324634secondlidfndsfdsfdsfdthirdlinedsfsdf