1, in case the mouse strays off the top
1, A
1, B
3, C
4, D
4, E
5, F
7, G
8, H
8, I
8, J
9, K
9, L
9, M
11, N
12, 0
12, PQ
13, R
13, S
14, T
15, U
15, V
15, W
16, X
17, YZ
17, in case the mouse strays off the bottom