To make a pair of identical cylindrical tin buckets without a lid, the diameter of the bottom surface is 20 cm, and the height is 40 cm. How many square decimeters of tin bucket should be used at least?
做一对完全相同的圆柱形无盖铁皮水桶，底面直径是20厘米，高40厘米，至少要用多少平方分米铁皮？
<gadget id="calculator">3.14 * 20 * 40</gadget>
<output>2_512</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">2_512 + 314</gadget>
<output>2_826</output>

<gadget id="calculator">2 / 100</gadget>
<output>1/50 = around 0.02</output>

<gadget id="calculator">2_826 * (1/50)</gadget>
<output>1_413/25 = around 56.52</output>

<result>1_413/25 = around 56.52</result>