Master Wang wants to make a cylindrical ventilation pipe with a bottom diameter of 2 decimeters and a height of 9 decimeters. How many square decimeters of iron sheet is needed at least?
王师傅要做一个底面直径2分米，高9分米的圆柱形通风管，至少需要多少平方分米的铁皮？
<gadget id="calculator">3.14 * 2 * 9</gadget>
<output>56.52</output>

<result>56.52</result>