7
0 0 0 0 2 4 0
0 0 5 0 0 0 0
0 3 0 0 0 0 0
0 1 0 0 0 0 0
2 0 0 0 0 0 3
0 0 0 0 7 0 0
0 0 2 1 0 0 0
