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: [21.531, 221.161, -31.194]
Example Output: 70.499

Example Input: [-31.252, 246.934, 96.512, 19.356, -50.759, 134.528, 176.914, 17.007, 171.802]
Example Output: 86.782

Example Input: [-55.955, 95.939, 147.531, 78.429, -66.582, -73.494, -88.544]
Example Output:
5.332