The radius of the wheel of a car is 0.5 meters, how many meters does it advance in one revolution?
一辆汽车的车轮半径是0.5米，它滚动一周前进多少米．
<gadget id="calculator">3.14 * 2 * 0.5</gadget>
<output>3.14</output>

<result>3.14</result>