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: [70.568, -80.778]
Example Output: -5.105

Example Input: [219.769, -36.26, 3.121, -22.5, 124.372]
Example Output: 57.7

Example Input: [-89.26, 23.797, 193.061]
Example Output:
42.533