A certain village primary school needs 30 iron-skin furnace cylinders (equivalent to ventilation pipes) with a bottom surface diameter of 10 cm and a length of 2 decimeters. Please calculate how many square centimeters of iron sheets are needed to make these furnace cylinders?
某村小学需30个底面直径10厘米，长2分米的铁皮炉筒(相当于通风管)，请你计算一下制做这些炉筒大约需要铁皮多少平方厘米？
<gadget id="calculator">2 * 10</gadget>
<output>20</output>

<gadget id="calculator">3.14 * 10 * 20 * 30</gadget>
<output>18_840</output>

<result>18_840</result>