Aunt Wang wanted to draw the largest square to plant vegetables in a rectangular field with a length of 20 meters, and fence the rest of the land to raise chickens. How many meters of fence are needed.
王大妈想在一个长为20米的长方形地里，先画出一个最大的正方形地种菜，剩下的地用篱笆围起来养鸡．共需篱笆多少米．
<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<result>40</result>