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: [-9.301, -10.629, 88.777, 68.965]
Example Output: 34.453

Example Input: [155.467, -40.717, -24.529, -22.608, 38.752]
Example Output: 21.273

Example Input: [126.705, 55.594, 168.974, 134.593, 82.585, 39.393]
Example Output:
101.307