There are 20 people standing on each side of a square array, (there are people at all four vertices), then how many people are there in this square array?
一个方阵每边站20人，(四个顶点都有人)，那么这个方阵一共有多少人．
<gadget id="calculator">20 * 20</gadget>
<output>400</output>

<result>400</result>