A square cardboard with an area of 540 square centimeters, cut off the four corners to make a cubic carton without a cover, what is the minimum square centimeter of the carton?
一张正方形的纸板，面积为540平方厘米，剪去四个角后，做成一个无盖的立方体纸盒，这个纸盒的用料至少是多少平方厘米？
<gadget id="calculator">5 * 5 * 4</gadget>
<output>100</output>

<gadget id="calculator">540 - 100</gadget>
<output>440</output>

<result>440</result>