How many square meters of tin is needed to make a cylindrical tin ventilation pipe with a length of 4 meters and a diameter of the nozzle of 0.2 meters.
做一根长4米、管口直径为0.2米的圆柱形白铁皮通风管，至少需要白铁皮多少平方米．
<gadget id="calculator">3.14 * 0.2 * 4</gadget>
<output>2.512</output>

<result>2.512</result>