print "$a[$_*3+2] " for (0..$#a/3);
print join ' ', @a[map {$_*3+2} (0..$#a/3)];

##</code><code>##

print "$a[$_*3-1] " for (1..@a/3); print "\n";
print join ' ', @a[map {$_*3-1} (1..@a/3)]; print "\n";