Make a pair of cylindrical tin buckets without a lid, the height is 24 cm, and the diameter of the bottom is 20 cm. How many square centimeters of iron sheet is needed at least?
做一对无盖的圆柱形铁皮水桶，高是24厘米，底面直径是20厘米．至少需要铁皮多少平方厘米？
<gadget id="calculator">3.14 * 20 * 24</gadget>
<output>1_507.2</output>

<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 ** 2</gadget>
<output>100</output>

<gadget id="calculator">3.14 * 100</gadget>
<output>314</output>

<gadget id="calculator">1_507.2 + 314</gadget>
<output>1_821.2</output>

<gadget id="calculator">1_821.2 * 2</gadget>
<output>3_642.4</output>

<result>3_642.4</result>