20. A chip is placed on one of the squares of a $7 \times 7$ board. It is allowed to sequentially place new chips on empty squares, but in such a way that each square on which the next chip is placed shares a side with no more than one already occupied square. What is the maximum number of chips that can be on the board after several such operations?

## 9th grade
93.20. Answer. 36 chips.