Plant trees around a square flower bed. It is required to plant one tree at each of the four vertices, and only 10 trees are planted on each side. How many trees are planted in total?
在一个正方形花坛的四周栽树，要求4个顶点各栽1棵，每边只栽10棵，共栽了多少棵树．
<gadget id="calculator">10 * 4</gadget>
<output>40</output>

<gadget id="calculator">40 - 4</gadget>
<output>36</output>

<result>36</result>