Plant trees around a square flower bed, one tree of each kind at the four vertices, and 5 trees on each side, how many trees are planted in total
在一个正方形花坛四周种树，四个顶点各种一棵，每边种5棵，共种多少棵
<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<gadget id="calculator">20 - 4</gadget>
<output>16</output>

<result>16</result>