Xiaohong has two small sticks, which are 15cm and 7cm long respectively. If a small stick is combined to form an isosceles triangle, what is the length of the third small stick in cm?
小红有两根小棒，分别长15cm和7cm，如果配一根小棒来拼成一个等腰三角形，第三根小棒的长度是多少cm．
<result>15</result>