A cuboid fuel tank is 1 meter long, 0.5 meters wide, and 0.4 meters high. How many square meters of iron sheet should be used at least to make such a pair of fuel tanks?
长方体油箱长1米，宽0.5米，高0.4米．做这样的一对油箱至少要用多少平方米的铁皮？
<gadget id="calculator">1 * 0.5</gadget>
<output>0.5</output>

<gadget id="calculator">0.5 * 0.4</gadget>
<output>0.2</output>

<gadget id="calculator">0.4 * 1</gadget>
<output>0.4</output>

<gadget id="calculator">0.5 + 0.2 + 0.4</gadget>
<output>1.1</output>

<gadget id="calculator">1.1 * 2</gadget>
<output>2.2</output>

<gadget id="calculator">2.2 * 2</gadget>
<output>4.4</output>

<result>4.4</result>