7
 0  0  0  0  0  0  0
-1  0  0  0  0  0  0
 0 -1  0  0 +1  0  0
 0  0 -1  0 +1  0  0
 0  0  0 -1 +1  0  0
 0 +1 +1 +1  0  0  0
 0  0  0  0  0  0  0