A mailbox was newly installed at the entrance of Guanghua Street. Its length is 50cm, width is 40cm, and height is 78cm. How much iron sheet is needed to make such a mailbox?
光华街口新装了一个邮箱，它的长是50cm，宽是40cm，高是78cm，做这样的一个邮箱需要多少铁皮？
<gadget id="calculator">50 * 40</gadget>
<output>2_000</output>

<gadget id="calculator">40 * 78</gadget>
<output>3_120</output>

<gadget id="calculator">78 * 50</gadget>
<output>3_900</output>

<gadget id="calculator">2_000 + 3_120 + 3_900</gadget>
<output>9_020</output>

<gadget id="calculator">9_020 * 2</gadget>
<output>18_040</output>

<result>18_040</result>