A sheep is tied with a 2m long rope under a tree, what is the maximum area that the sheep can eat grass?
在一棵树下用2m长的绳子拴着一只羊，这只羊可以吃到草的面积最大是多少？
<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<result>12.56</result>