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: [21.659, 63.646, -97.361]
Example Output: -4.019

Example Input: [-4.527, 190.006, 207.554, 178.685, -20.05, 13.024, 190.617, 37.539]
Example Output: 99.106

Example Input: [71.39, 133.73, -86.265, 237.963, 228.337, 220.263, 127.766, 174.117]
Example Output:
138.413