On the following chessboard every white square meets at least two red squares.

[![enter image description here](https://i.stack.imgur.com/U9cH1.png)](https://i.stack.imgur.com/U9cH1.png)

Let's paint a new chessboard so that every white square meets *exactly* two red square. Every square should be painted either red or white. It is clearly possible from the following chessboard.

[![enter image description here](https://i.stack.imgur.com/kUIlv.png)](https://i.stack.imgur.com/kUIlv.png)

But, too many squares were painted red. What is the minimal number of squares should be painted red?