There is a circular flowerbed with a radius of 5 meters. If it is surrounded by a fence, how long should the fence be at least?
有一个圆形花圃，半径为5米，如果用篱笆把它围起来，至少要多长的篱笆？
<gadget id="calculator">2 * 3.14 * 5</gadget>
<output>31.4</output>

<result>31.4</result>