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: [-81.432, -63.059, 150.144, 55.203, 215.405, -89.797, 72.946]
Example Output: 37.059

Example Input: [17.197, 152.985, 73.815]
Example Output: 81.332

Example Input: [-93.279, 77.253]
Example Output:
-8.013