Given NxN matrix with integer numbers.
Find the greatest number for every 3x3 matrix.

update example

example.1
[[1,2,3],
[4,5,6],
[7,8,9]]

ans:
[9]

example.2
[[1,2,3,6],
[5,2,4,1],
[3,4,2,3],
[8,2,1,4]]

ans:
[[5,6],
[8,4]]