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: [-96.229, 200.453]
Example Output: 52.112

Example Input: [128.152, 95.16, 70.113, -16.853]
Example Output: 69.143

Example Input: [217.81, 223.973, 80.273, 20.718]
Example Output:
135.694