The bottom of the chimney is 20 cm in diameter and 0.8 m long. To make a chimney like 50 knots, if the joints are ignored, how many square meters of iron sheets are needed at least?
烟囱的底面直径是20厘米，长0.8米．作50节这样的烟囱，如果接头处忽略不计，至少需要铁皮多少平方米？
<gadget id="calculator">50 / 10_000</gadget>
<output>1/200 = around 0.005</output>

<gadget id="calculator">3.14 * 20 * 0.8 * 100 * (1/200)</gadget>
<output>25.12</output>

<result>25.12</result>