How many square meters of iron sheet is needed to make 20 sections of iron chimney with a length of 1 meter and a bottom radius of 10 cm?
做20节长1米，底面半径是10厘米的铁皮烟囱，至少需要多少平方米的铁皮？
<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">2 * 3.14 * (1/10) * 1 * 20</gadget>
<output>12.56</output>

<result>12.56</result>