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: [-31.252, 246.934, 96.512, 19.356, -50.759, 134.528, 176.914, 17.007, 171.802]
Example Output: 86.782

Example Input: [34.678, 109.562]
Example Output: 72.12

Example Input: [158.078, -10.918, 129.671]
Example Output:
92.277