A circular hoop has a diameter of 20 cm, how much wire is needed to make such a hoop.
一个圆形的铁环，直径是20厘米，做一个这样的铁环需要多少的铁丝．
<gadget id="calculator">3.14 * 20</gadget>
<output>62.8</output>

<result>62.8</result>