When drawing a circle, the distance between the two feet of the compass is 4 cm. What is the circumference of the circle?
画圆时，圆规两脚间的距离是4厘米，这个圆的周长是多少．
<gadget id="calculator">3.14 * 4 * 2</gadget>
<output>25.12</output>

<result>25.12</result>