A cow is tied to a meadow. If the rope to tie the cattle is 4 meters long (excluding the knotted part). How many square meters of grass can this cow eat at most?
在一片草地上拴着一头牛．若拴牛的绳子长4米(不含打结部分)．这头牛最多可以吃到多少平方米的草？
<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

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

<result>50.24</result>