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: [159.381, -84.046]
Example Output: 37.668

Example Input: [-38.715, 205.647, 66.034, 49.8, -92.051, 111.017, 149.689]
Example Output: 64.489

Example Input: [167.292, 188.961, 203.661, 86.355, 217.931, -27.422]
Example Output:
139.463