The radius of a circular flower bed is 2.5 meters, and a fence is surrounded 0.5 meters away from the flower bed. What is the total length of the fence in meters?
一个圆形花坛的半径是2.5米，在离花坛0.5米处围上一圈栅栏，栅栏的全长是多少米
<gadget id="calculator">2.5 + 0.5</gadget>
<output>3</output>

<gadget id="calculator">2 * 3.14 * 3</gadget>
<output>18.84</output>

<result>18.84</result>