How many square decimeters of iron sheet are needed to make a cylinder with a length of 20 decimeters and a base radius of 10 centimeters.
做一个长20分米，底面半径10厘米圆柱体的通风管需要多少平方分米铁皮．
<gadget id="calculator">10 / 10</gadget>
<output>1</output>

<gadget id="calculator">3.14 * 1 * 2 * 20</gadget>
<output>125.6</output>

<result>125.6</result>