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: [-11.211, 9.955, 208.942, 124.097, 118.282, 65.001]
Example Output: 85.844

Example Input: [-20.155, -42.404]
Example Output: -31.28

Example Input: [132.035, 139.298]
Example Output:
135.666