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: [157.423, -98.775, -67.748, 25.759, 24.697, 150.289, -68.457, 212.57, -9.355]
Example Output: 36.267

Example Input: [65.591, -56.104, -28.389, -22.521]
Example Output: -10.356

Example Input: [-16.768, 0.229, 14.955, -32.161, -40.159, -81.113, 34.071]
Example Output:
-17.278