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: [78.523, 239.098, 9.698, 69.94]
Example Output: 99.315

Example Input: [120.236, 116.311, -13.268]
Example Output: 74.426

Example Input: [-60.49, -81.703, -53.741]
Example Output:
-65.311