To make a chimney with a bottom diameter of 10 decimeters and a length of 40 decimeters, at least how many square decimeters of iron sheet is needed.
做一节底面直径为10分米，长40分米的烟筒，至少需要多少平方分米铁片．
<gadget id="calculator">3.14 * 10 * 40</gadget>
<output>1_256</output>

<result>1_256</result>