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: [-7.892, -43.609, 46.236, -78.213, -76.066]
Example Output: -31.909

Example Input: [-2.869, -88.698, 21.318]
Example Output: -23.416

Example Input: [210.354, 91.127, 51.505, -84.377, -68.134, 100.685, 241.744, -99.032, -56.574, -85.971]
Example Output:
30.133