A sheep is tied with a rope 4 meters long, surrounded by grass, what is the maximum area of grass that the lamb can eat?
用4米长的绳子拴一只羊，周围全是草地，小羊能吃到的草地最大面积是多少？
<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

<gadget id="calculator">3.14 * 16</gadget>
<output>50.24</output>

<result>50.24</result>