In this task you will be given a list of numbers and you need to find the mean (average) of that list. The mean of a list can be found by summing every number in the list then dividing the result by the size of that list. The output should be rounded to 3 decimal places.

Example Input: [169.421, 88.16]
Example Output: 128.791

Example Input: [-21.77, 172.703, -31.807, 129.587, 84.624, 14.279]
Example Output: 57.936

Example Input: [157.896, -9.242, -34.082]
Example Output:
38.191