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: [37.853, 78.283, 143.128, 82.561, 181.661, -89.154, 50.037]
Example Output: 69.196

Example Input: [246.744, 206.484, 194.841]
Example Output: 216.023

Example Input: [11.382, -86.442, -28.625]
Example Output:
-34.562