From a piece of rectangular paper with a length of 15 cm and a width of 9 cm, cut out the largest square and turn it into a small rectangle. Then cut a largest square from this small rectangle, what is the perimeter of this square in centimeters?
从一张长15厘米、宽9厘来的长方形纸上，剪掉一个最大的正方形后变成一个小长方形．再从这个小长方形上剪一个最大的正方形，这个正方形的周长是多少厘米？
<gadget id="calculator">15 - 9</gadget>
<output>6</output>

<gadget id="calculator">6 * 4</gadget>
<output>24</output>

<result>24</result>