How many square meters of tin chimney is needed to make a chimney with a length of 5 meters and a diameter of 0.5 meters at the bottom?
做一节长5米，底面直径是0.5米的铁皮烟囱，至少需要多少平方米的铁皮？
<gadget id="calculator">3.14 * 0.5 * 5</gadget>
<output>7.85</output>

<result>7.85</result>