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: [218.807, 72.849, 7.838, 124.81, 45.929, 239.888]
Example Output: 118.354

Example Input: [246.278, 103.84, 214.867, -73.466, 230.048, -72.322, 172.891, 212.306, -78.335, 122.406]
Example Output: 107.851

Example Input: [-75.309, 13.595, -21.503]
Example Output:
-27.739