6
    1-----------------
         1         0         0
         0         1         0
         0         0         1
    2-----------------
         0         0         1
         1         0         0
         0         1         0
    3-----------------
         0         1         0
         0         0         1
         1         0         0
    4-----------------
         0         1         0
         1         0         0
         0         0         1
    5-----------------
         1         0         0
         0         0         1
         0         1         0
    6-----------------
         0         0         1
         0         1         0
         1         0         0
 -------------------------------