It is 10 decimeters to make 20 cylindrical ventilating pipes with a length of 50 decimeters, how many square decimeters of iron sheet should be used at least?
制作20个底面半径是10分米，长50分米的圆柱形通风管，至少要用多少平方分米铁皮？
<gadget id="calculator">3.14 * 10 * 2 * 50</gadget>
<output>3_140</output>

<gadget id="calculator">3_140 * 20</gadget>
<output>62_800</output>

<result>62_800</result>