3
9 x x x x 4 x 8 x
x x x 2 x x x x 3
x x 5 x 7 x 6 x x
8 x x x x x x x 9
x x 3 x 1 x 5 x x
x 6 x x x x x 4 x
x 7 x x 6 x x x x
4 x x x x 5 x 1 x
x x 2 3 x x x x x