Plant trees around the four corners of a square flower bed, and plant 5 trees on each side. How many trees are planted in total?
在一个正方形花坛的四周种树，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>