18,4:
20--------0++++0++++-0-+0--+0++---++++++---0---0-+0---++0++++0--++--++0
3[[4,6,5,7,0,2,1,3],[0,4,2,6,1,5,3,7],[6,7,4,5,2,3,0,1],[7,6,5,4,3,2,1,0]]
4