Hello! Can you help me with this task (I came up with it myself).

Task: You get an NxN matrix consisting of zeros and ones. You also have an operation where you can 3x3 submatrix into zeros. Your task is to convert all ones to zeros with as few operations as possible.

The size of N is unknown, but I was aiming for N <= 2000.

Input: You get integer N and matrix of size NxN. It can only have zeros and ones.

Output: Print integer, the minimal number of operations.

Example:

5

00100

11111

00100

00100

00000

Answer: 2