4
14 0 9 7    0 0 0 2   12 16 6 0      5 1 8 0
0 8 1 12    7 4 0 3   0 13 0 0       0 0 0 0
6 16 0 0    11 0 0 8  14 0 5 7      13 0 9 0
3 10 0 15   0 0 0 0   1 0 0 0        0 0 4 0
0 0 0 0     0 0  0 0  0 0 0 0       0 0 0 0
0 0 0 0     0 0  0 0  0 0 0 0       0 0 0 0
0 0 0 0     0 0  0 0  0 0 0 0       0 0 0 0
0 0 0 0     0 0  0 0  0 0 0 0       0 0 0 0
0 0 0 0     0 0  0 0  0 0 0 0       0 0 0 0
0 0 0 0     0 0  0 0  0 0 0 0       0 0 0 0
0 0 0 0     0 0  0 0  0 0 0 0       0 0 0 0
0 0 0 0     0 0  0 0  0 0 0 0       0 0 0 0
0 0 0 0     0 0  0 0  0 0 0 0       0 0 0 0
0 0 0 0     0 0  0 0  0 0 0 0       0 0 0 0
0 0 0 0     0 0  0 0  0 0 0 0       0 0 0 0
0 0 0 0     0 0  0 0  0 0 0 0       0 0 0 0