There is a rectangular iron sheet with a length of 12.56 decimeters and a width of 5 decimeters. Master Wang used it to make the side of a cylindrical bucket. If you want to make its volume the largest, and then match it with a bottom, how many square decimeters of iron sheet is needed at least?
有一块长12.56分米、宽5分米的长方形铁皮，王师傅用它做一个圆柱形水桶的侧面．如果要使它的容积最大，再配一个底，至少还要多少平方分米的铁皮？
<gadget id="calculator">12.56 / 3.14 / 2</gadget>
<output>2</output>

<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<result>12.56</result>