There is a square tin box containing biscuits. The bottom is square, the side length is 20 cm, and the height is 30 cm. The tin box is surrounded by trademarks. What is the area of the trademark in square centimeters?
有一个装饼干的正方形铁盒，底面是正方形，边长是20厘米，高是30厘米，这个铁盒四周印满商标，商标的面积是多少平方厘米？
<gadget id="calculator">20 * 4 * 30</gadget>
<output>2_400</output>

<result>2_400</result>