To process a cylindrical chimney with a bottom diameter of 20cm and a height of 90cm, at least how much iron sheet is required in cm**2.
加工一节底面直径是20cm，高是90cm的圆柱形烟囱，至少需要铁皮多少cm**2．
<gadget id="calculator">3.14 * 20 * 90</gadget>
<output>5_652</output>

<result>5_652</result>