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: [15.799, 6.545, 101.018, -76.074, 51.291, -58.732, 131.857, -36.93, 131.423]
Example Output: 29.577

Example Input: [203.498, -79.59, -73.767, -65.942, -8.693]
Example Output: -4.899

Example Input: [-56.355, -68.135, 113.376, 3.683, -39.11, -79.627, -71.223, -10.187, 71.098]
Example Output:
-15.164