This is a puzzle game for training your skill of mental calculation.

Rules

Erase number plates by touching squares of 2×2 plates.

If the total of figures of plates touched is 20, you can erase it. 

Otherwise, four plates rotate clockwise.

The time limit gauge is expanding while you don't erase any plates. And when it becomes full, the game is over.

When 20 plates or more are erased, new plates appears, and the time limit becomes severe.