Minzu Hope Primary School plans to provide a water cup for each of the 180 primary school students who live in the school. After market research, it is determined that a water cup is 5 yuan each. Supermarket A offers a 10% discount, and Supermarket B offers "buy 8 get 1 free". Please help me figure it out, which supermarket is the most cost-effective to buy?
民族希望小学准备为住校的180名小学生每人配一个水杯，经市场调查后确定配5元一个的水杯．A超市打九折出售，B超市"买八送一’．请你帮忙算算，到哪个超市购买划算？
<result>180</result>