To make a tin chimney with a section length of 1 meter and a bottom diameter of 20 cm, how many square meters of tin chimney is needed at least?
做一节长1米，底面直径是20厘米的铁皮烟囱，至少需要多少平方米的铁皮？
<gadget id="calculator">100 / 10_000</gadget>
<output>1/100 = around 0.01</output>

<gadget id="calculator">3.14 * 20 * 1 * (1/100)</gadget>
<output>0.628</output>

<result>0.628</result>