A square with the smallest square centimeter in area can be covered with a rectangular piece of paper with a length of 5 cm and a width of 4 cm.
用长5cm、宽4cm的长方形纸可以正好铺满面积最小多少平方厘米的正方形．
<gadget id="calculator">5 * 4</gadget>
<output>20</output>

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

<result>400</result>