What is the area of a circular flower bed with a diameter of 20 meters?
一个直径20米的圆形花坛，面积是多少．
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 ** 2</gadget>
<output>100</output>

<gadget id="calculator">3.14 * 100</gadget>
<output>314</output>

<result>314</result>