Inspired by Chung Kevin

There are nine 3×3 3 \times 3 sub-grids in the 5×5 5 \times 5 grid. If at most 5 out of 9 unit squares are shaded blue in any 3×3 3 \times 3 sub-grid, what is the maximum number of unit squares in the 5×5 5 \times 5 grid that can be shaded blue?


Inspiration

Note: An example of how the grid can be shaded is shown to the right.

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