To make a chimney with a bottom diameter of 20cm and a length of 1m, at least how many dm**2 iron sheets are needed.
做一节底面直径是20cm，长1m的烟囱，至少需要多少dm**2的铁皮．
<gadget id="calculator">1 * 100</gadget>
<output>100</output>

<gadget id="calculator">100 / 100</gadget>
<output>1</output>

<gadget id="calculator">3.14 * 20 * 1</gadget>
<output>62.8</output>

<result>62.8</result>