How many square decimeters of iron sheet is needed to make an oil drum with a height of 20 decimeters and a bottom radius of 4 decimeters?
用铁皮制作一个高20分米，底面半径是4分米的油桶，需要铁皮多少平方分米？
<gadget id="calculator">3.14 * 4 * 2 * 20</gadget>
<output>502.4</output>

<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

<gadget id="calculator">3.14 * 16 * 2</gadget>
<output>100.48</output>

<gadget id="calculator">502.4 + 100.48</gadget>
<output>602.88</output>

<result>602.88</result>