To make a cuboid container without a cover, the length is 20 cm, the width is 15 cm, and the height is 10 cm. What is the minimum square centimeter of cardboard needed?
做一个无盖的长方体容器，长20厘米，宽15厘米，高10厘米，至少需要多少平方厘米的硬纸板？
<gadget id="calculator">20 * 10</gadget>
<output>200</output>

<gadget id="calculator">15 * 10</gadget>
<output>150</output>

<gadget id="calculator">200 + 150</gadget>
<output>350</output>

<gadget id="calculator">350 * 2</gadget>
<output>700</output>

<gadget id="calculator">20 * 15</gadget>
<output>300</output>

<gadget id="calculator">700 + 300</gadget>
<output>1_000</output>

<result>1_000</result>