The length of a section of cylindrical ventilation pipe is 10dm, and the radius of the nozzle is 5dm. How much dm**2 iron sheets are needed to make such a section of ventilation pipe.
一节圆柱形通风管长10dm，管口半径5dm，制成一节这样的通风管需多少dm**2的铁皮．
<gadget id="calculator">2 * 3.14 * 5 * 10</gadget>
<output>314</output>

<result>314</result>