There is a square swimming pool, 20 trees are planted on each side of it, one of each kind at the four corners, how many are planted in total?
有一个正方形游泳池，在它的每边都种上20棵树，四个角各种一棵，共种多少．
<gadget id="calculator">20 * 4</gadget>
<output>80</output>

<gadget id="calculator">80 - 4</gadget>
<output>76</output>

<result>76</result>