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: [-7.892, -43.609, 46.236, -78.213, -76.066]
Example Output: -31.909

Example Input: [66.037, 30.958, 124.853]
Example Output: 73.949

Example Input: [231.74, 142.135, 60.231, -34.154, 111.503, -84.615, 186.711, 52.235, 43.888, -20.096]
Example Output:
68.958