The specifications of a mobile phone battery are 40mm-41mm-6.5mm. Xiaoxiao wants to use cardboard to make a box without a cover to hold two such batteries. How many square millimeters of cardboard do you need at least?
某款手机电池的规格为40mm-41mm-6.5mm，笑笑要用硬纸板做一个无盖的盒子来装两块这样的电池，至少需要多少平方毫米的硬纸板？
<gadget id="calculator">40 * 41</gadget>
<output>1_640</output>

<gadget id="calculator">6.5 * 2</gadget>
<output>13</output>

<gadget id="calculator">40 * 13</gadget>
<output>520</output>

<gadget id="calculator">41 * 13</gadget>
<output>533</output>

<gadget id="calculator">520 + 533</gadget>
<output>1_053</output>

<gadget id="calculator">1_053 * 2</gadget>
<output>2_106</output>

<gadget id="calculator">1_640 + 2_106</gadget>
<output>3_746</output>

<result>3_746</result>