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

Example Input: [222.94, 54.014, 232.208, -16.089, 214.915, 2.232]
Example Output: 118.37

Example Input: [203.883, -95.013, 151.386, 244.084, 60.393]
Example Output:
112.947