Cut out the largest square from a rectangular piece of paper with a length of 3 cm and a width of 2.5 cm, and find the perimeter of the square.
从一张长3厘米、宽2.5厘米的长方形纸片上剪下一个最大的正方形，求这个正方形的周长．
<gadget id="calculator">2.5 * 4</gadget>
<output>10</output>

<result>10</result>