$ cat in.txt 
1 22 3 -4

a
b c
d e f
g h i j
k l m n o
$ perl -anle 'print "@F[map $#F-$_*2, 0..$#F/2]"' in.txt 
-4 22

a
c
f d
j h
o m k

##</code><code>##

while (<>) {
	my @fields = split;
	for (my $i=$#fields; $i>=0; $i-=2) {
		print "$fields[$i] ";
	}
	print "\n";
}