Plant trees around a square pond, plant 8 trees on each side, and plant one tree at each corner, how many trees are planted in total?
在一个正方形池塘的四周栽树，每边种8棵，且四个角都要种一棵，一共种多少树．
<gadget id="calculator">8 * 4</gadget>
<output>32</output>

<gadget id="calculator">32 - 4</gadget>
<output>28</output>

<result>28</result>