f=lambda m,x:m and(x&1and m.pop(0)or m.pop(0)[::-1])+f(m,x+1)
print(f([[4, 3, 2, 1], [5, 6, 7, 8], [12, 11, 10, 9], [13, 14, 15, 16]],0))
Zj1sYW1iZGEgbSx4Om0gYW5kKHgmMWFuZCBtLnBvcCgwKW9yIG0ucG9wKDApWzo6LTFdKStmKG0seCsxKQpwcmludChmKFtbNCwgMywgMiwgMV0sIFs1LCA2LCA3LCA4XSwgWzEyLCAxMSwgMTAsIDldLCBbMTMsIDE0LCAxNSwgMTZdXSwwKSk=
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]