题目描述 Larry graduated this year and finally has a job. He's making a lot of $ money $, but somehow never seems to have enough. Larry has decided that he needs to grab hold of his $ financial $ portfolio and solve his $ financing $ problems. The first step is to figure out what's been going on with his $ money $. Larry has his $ bank $ $ account $ statements and wants to see how much $ money $ he has. Help Larry by writing a $ program $ to take his $ closing $ $ balance $ from each of the past $ twelve $ $ months $ and calculate his $ average $ $ account $ $ balance $. 输入格式 Each case will be $ twelve $ lines. Each line will contain the $ closing $ $ balance $ of his $ bank $ $ account $ for a particular $ month $. Each $ number $ will be $ positive $ and displayed to the $ penny $. No $ dollar $ sign will be included. 输出格式 For each case, the $ output $ will be a single $ number $, the $ average $ ($ mean $) of the $ closing $ $ balances $ for the $ twelve $ $ months $. It will be $ rounded $ to the nearest $ penny $, preceded immediately by a $ dollar $ sign, and followed by the $ end-of-line $. There will be no other $ spaces $ or $ characters $ in the $ output $. 输入样例 100.00 489.12 12454.12 1234.10 823.05 109.20 5.27 1542.25 839.18 83.99 1295.01 1.75 输出样例 $1581.42