Grandma Liu wants to build a square chicken pen with wooden slats against the wall. The side length of the chicken pen is 5 meters. Please help her calculate the length of the fence?
刘奶奶要靠着墙用木条围起一个正方形的养鸡圈，鸡圈的边长有5米，请帮她算算围起的篱笆长有多少米？
<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<result>15</result>