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: [9.392, -80.549]
Example Output: -35.579

Example Input: [38.343, 177.478, 120.174, -74.923, 98.159]
Example Output: 71.846

Example Input: [50.821, -15.96, 192.878, 22.51, 231.681, 249.66]
Example Output:
121.932