To make a ventilation pipe with a bottom diameter of 20 cm and a length of 60 cm, at least how many square centimeters of iron sheets are needed.
做一节底面直径是20厘米，长60厘米的通风管，至少需要铁皮多少平方厘米．
<gadget id="calculator">3.14 * 20 * 60</gadget>
<output>3_768</output>

<result>3_768</result>