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: [-57.838, -63.616, 49.646, -45.262, 73.1, -82.399, 47.168]
Example Output: -11.314

Example Input: [220.903, 155.959]
Example Output: 188.431

Example Input: [-9.76, 15.211, 221.876, 199.639, -25.325, 213.489, -14.541, 87.066]
Example Output:
85.957