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: [-6.992, -36.177, -95.203, 87.142]
Example Output: -12.808

Example Input: [183.332, -51.581, -15.684, 140.965, 37.376, 37.734, 71.356]
Example Output: 57.643

Example Input: [-87.129, 165.353, 37.001, 249.42]
Example Output:
91.161