To make a cuboid iron box without a cover, its length is 2.5 decimeters, its width and height are both 1 decimeter, at least how many square decimeters of iron sheet is needed?
做一个无盖的长方体铁盒，它的长是2.5分米，宽和高都是1分米，至少需用多少平方分米的铁皮？
<gadget id="calculator">2.5 * 1</gadget>
<output>2.5</output>

<gadget id="calculator">2.5 * 1 * 2</gadget>
<output>5</output>

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

<gadget id="calculator">2.5 + 5 + 2</gadget>
<output>9.5</output>

<result>9.5</result>