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: [199.974, 2.205, 197.996, 172.426, 182.153, 42.045, 53.238, 18.021, 83.903]
Example Output: 105.773

Example Input: [128.916, 203.766]
Example Output: 166.341

Example Input: [-63.878, 1.247]
Example Output:
-31.316