2017百度春招：度度熊想去商场买一顶帽子，商场里有N顶帽子，有些帽子的价格可能相同。度度熊想买一顶价格第三便宜的帽子，问第三便宜的帽子价格是多少？(2017 Baidu Spring Recruit: degree of bears want to go to the mall to buy a hat, there are N hat in the mall, some hats may be the same price. The degree of bear want to buy a