A sheep is tied to a stake in the grass. If the length of the rope is 2 meters, what is the maximum area of grass that the sheep can eat?
把一只羊拴在草地的木桩上，如果绳长2米，这只羊吃到草的最大面积是多少平方米？
<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

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

<result>12.56</result>