A rectangular parallelepiped carton with a square base, if its sides are unfolded, it is exactly a square with a side length of 20 decimeters. What is the surface area of this rectangular parallelepiped carton?
一个底面是正方形的长方体纸盒，将它的侧面展开正好是一个边长为20分米的正方形，这个长方体纸盒的表面积是多少？
<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">5 * 5 * 2</gadget>
<output>50</output>

<gadget id="calculator">20 * 20</gadget>
<output>400</output>

<gadget id="calculator">50 + 400</gadget>
<output>450</output>

<result>450</result>