piece of rectangular paper with a length of 18 cm and a width of 10 cm can be folded into a square. What is the maximum perimeter of this square in cm?
一张长18厘米、宽10厘米的长方形纸，可以折成一个正方形，这个正方形周长最大是多少厘米．
<gadget id="calculator">10 * 4</gadget>
<output>40</output>

<result>40</result>