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: [-19.26, 130.53, 225.367, 179.475, -63.39]
Example Output: 90.544

Example Input: [142.225, 243.809, -41.935, 96.795, -99.067, 222.292, 113.486, 143.726]
Example Output: 102.666

Example Input: [178.81, 155.118, 83.979]
Example Output:
139.302