Financial Management
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Leila graduated this year and finally has a job.  She's making a lot of 
money, but somehow never seems to have enough.  Leila has decided that 
she needs to grab hold of her financial portfolio and solve her financing 
problems.  The first step is to figure out what's been going on with her 
money.  Leila has her bank account statements and wants to see how much 
money she has.  Help Leila by writing a program to take his closing balance 
from each of the past twelve months and calculate her average account balance.

Input
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The input will be twelve lines.  Each line will contain the closing balance 
of her bank account for a particular month.  Each number will be positive 
and displayed to the penny.  No dollar sign will be included.

Output
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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.

Sample Input
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100.00
489.12
12454.12
1234.10
823.05
109.20
5.27
1542.25
839.18
83.99
1295.01
1.75

Sample Output
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$1581.42