Use iron sheets to make 20 cylindrical chimneys of the same size. Each section is 8 decimeters long and the bottom diameter is 10 centimeters. How many square decimeters of iron sheets are needed at least?
用铁皮做20节同样大小的圆柱形烟囱，每节长8分米，底面直径是10厘米，至少需要铁皮多少平方分米？
<gadget id="calculator">10 / 10</gadget>
<output>1</output>

<gadget id="calculator">3.14 * 1 * 8 * 20</gadget>
<output>502.4</output>

<result>502.4</result>