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: [245.271, 40.965, 133.913, 212.104]
Example Output: 158.063

Example Input: [126.198, -70.303]
Example Output: 27.947

Example Input: [35.329, -23.551, -90.367, 226.117, 170.26, 6.137]
Example Output:
53.988