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: [21.531, 221.161, -31.194]
Example Output: 70.499

Example Input: [225.697, 75.029]
Example Output: 150.363

Example Input: [233.719, 11.512, 159.737, -55.121, 2.157]
Example Output:
70.401

