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: [76.889, 179.836, 105.364]
Example Output: 120.696

Example Input: [165.901, 226.337, -51.459, 118.136, 2.079, 66.231, 175.697, -84.018, 51.186, 165.388]
Example Output:
83.548