Niu Niu goes to the supermarket and wants to buy 9 ballpoint pens. There are two kinds of packaging. The single package costs 4 yuan each; the package of 9 pens costs 27 yuan per box. In your opinion, how to buy Niu Niu is a good deal?
牛牛到超市想买9支圆珠笔，有两种包装，单支的包装，4元一支；9支一盒的包装，每盒27元．你认为，牛牛怎样买合算？
<result>9</result>