A sheep is tied to a tree. The length of the rope from the tree to the neck of the sheep is 2 meters. What is the maximum area of grass that it can eat.
一只羊拴在树旁，树到羊颈间的绳长2米，它能吃到最大范围为多少平方米的草．
<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

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

<result>12.56</result>