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: [129.453, 232.284, -34.595]
Example Output: 109.047

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

Example Input: [169.253, 248.402, 138.613, 144.26, 116.446, -20.712, 98.286, -38.63, 150.489]
Example Output:
111.823