The base of a cuboid is a square with a perimeter of 20 decimeters, and its side view is also a square. What is the volume of this cuboid?
一个长方体的底面是周长为20分米的正方形，它的侧面展开图正好也是一个正方形，这个长方体的体积是多少立方分米．
<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">5 * 5 * 20</gadget>
<output>500</output>

<result>500</result>