To make a cylindrical iron bucket with a bottom diameter of 40cm and a height of 30cm, how much iron is needed at least?
做一个底面直径是40cm，高是30cm的圆柱形无盖铁皮水桶，至少需要多少铁皮？
<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<gadget id="calculator">20 ** 2</gadget>
<output>400</output>

<gadget id="calculator">3.14 * 400</gadget>
<output>1_256</output>

<gadget id="calculator">3.14 * 40 * 30</gadget>
<output>3_768</output>

<gadget id="calculator">1_256 + 3_768</gadget>
<output>5_024</output>

<result>5_024</result>