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: [-66.271, 56.586, -21.072, 136.915, 54.951, 112.054]
Example Output: 45.527

Example Input: [-98.361, -84.91]
Example Output: -91.636

Example Input: [-0.223, -81.443, 108.234, 35.865, -90.363, 30.802, -66.19, 245.018, 3.767]
Example Output:
20.607