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: [70.553, 193.054, 166.173, 115.812]
Example Output: 136.398

Example Input: [41.081, 166.314, -14.556, -84.648, -8.286]
Example Output: 19.981

Example Input: [217.458, 224.557, 176.324, -19.725]
Example Output:
149.653