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

Example Input: [-31.241, 73.981, 127.71, 166.275, 35.028, -10.432]
Example Output: 60.22

Example Input: [-99.355, -3.837, 155.693, 130.002, 4.319, 184.828, 199.546]
Example Output:
81.599