A piece of rectangular paper has a length of 9 cm and a width of 5 cm. Cut a largest square out of this rectangular paper. What is the perimeter of the square in cm?
一张长方形纸，长是9厘米，宽是5厘米，在这个长方形纸中剪一个最大的正方形，正方形的周长是多少厘米．
<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<result>20</result>