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: [108.26, -20.681, 127.479, -29.352]
Example Output: 46.426

Example Input: [139.608, 17.516, 100.5, -51.362, 57.462, -77.569, -95.41, -24.339, -96.579]
Example Output: -3.353

Example Input: [-19.13, 98.86, 158.686, 230.23]
Example Output:
117.161