CHECKER 4 4
[0,0,1,0,0,1] [1,0,2,0,1,1] [2,0,1,1,2,2]
[0,1,-1,1,0,2] [1,1,0,1,0,2] [3,1,2,2,3,3]
[0,2,0,3,1,3] [2,2,2,4,3,3]
[0,3,1,3,0,4] [1,3,0,4,1,4] [3,3,4,3,3,5]