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: [-17.141, 203.132, -6.872, 155.222, -99.642]
Example Output: 46.94

Example Input: [-17.026, 165.89]
Example Output: 74.432

Example Input: [-25.972, -50.621, -29.364, 33.0, 174.639, 55.518, 2.267, 157.02, 178.689]
Example Output:
55.02