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: [100.422, 199.731, 138.971, 95.515, 9.517]
Example Output: 108.831

Example Input: [-82.27, 46.742, -60.547, 97.652, 121.66, 104.393, -43.603, 125.281, 42.318, 200.514]
Example Output: 55.214

Example Input: [177.989, 115.566]
Example Output:
146.778