A box full of blocks and bubbles. One door. Rotate to empty it.

• Blocks are heavier than air. Bubbles are lighter than air.

• Pieces can only escape through the door on the top or bottom wall.

• A block on top of one bubble drags it down — they fall together.

• A block on top of two bubbles gets lifted up — they rise together.

Clear the box in as few rotations as possible.