To make a cylindrical ventilation pipe with a bottom diameter of 20cm and a length of 60cm, at least how many cm**2 iron sheets are needed.
做一节底面直径是20cm，长60cm的圆柱形通风管，至少需要多少cm**2铁皮．
<gadget id="calculator">3.14 * 20 * 60</gadget>
<output>3_768</output>

<result>3_768</result>