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: [17.197, 152.985, 73.815]
Example Output: 81.332

Example Input: [24.119, 239.006, 239.873, 236.27, 134.34]
Example Output: 174.722

Example Input: [-18.016, 247.669, 100.835, 180.329, -11.701, 46.576, 47.896, 175.095, 21.187]
Example Output:
87.763