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: [228.031, -85.617, 36.164]
Example Output: 59.526

Example Input: [219.879, -65.298, -87.086, 229.401, 94.505, 97.81, -89.529, -48.863, 2.922]
Example Output:
39.305