$8 \times 8$ chessboard such that no two of them attack each other?

What is the maximum number of knights you can place on a**Details and assumptions**

The knights are placed on distinct cells.

Two knights attack each other if they are one cell vertically and two cells horizontally apart or two cells vertically and one cell horizontally apart.

A $8 \times 8$ chessboard has $8^2= 64$ cells.

Here's an example of $2$ knights being placed on a $3 \times 3$ chessboard which attack each other.