There are some trees planted around a square pond, one tree is planted at each corner, and 8 trees are planted on each side. How many trees are planted in total?
一个正方形池塘四周栽了些树，四个角的都有1棵，每边栽8棵，一共栽了多少棵．
<gadget id="calculator">8 * 4</gadget>
<output>32</output>

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

<result>28</result>