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: [26.857, -69.553, -37.942]
Example Output: -26.879

Example Input: [230.375, -45.327, 112.137, 109.305]
Example Output: 101.622

Example Input: [136.136, 72.696, 63.517, 108.592, 188.638, 37.871, -64.559, 85.379, -13.679, -17.628]
Example Output:
59.696