For a round bucket, the mouth and bottom of the bucket are the same size, and the outer diameter is 5 decimeters. Now use iron wire to fasten the mouth and bottom of the bucket. How many decimeters of iron wire is needed at least?
一个圆形水桶，桶口和桶底都是一样大小的圆形，外直径是5分米，现在用铁丝将桶口和桶底箍紧，至少需要铁丝多少分米？
<gadget id="calculator">3.14 * 5 * 2</gadget>
<output>31.4</output>

<result>31.4</result>