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: [-2.869, -88.698, 21.318]
Example Output: -23.416

Example Input: [112.53, -67.079, 177.313, 230.482, 57.316, -37.564]
Example Output: 78.833

Example Input: [20.796, 39.383, -26.46, -27.224, 89.591, 87.502, 211.781, 127.87, 223.38]
Example Output:
82.958