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: [207.165, 246.399, 44.821, -21.671]
Example Output: 119.178

Example Input: [196.683, 97.538, 247.799, 203.036, 203.369, -15.737]
Example Output: 155.448

Example Input: [-12.636, 107.17, 200.315, 67.156, 28.809, 241.797, 197.193, 81.53, -90.008]
Example Output:
91.258