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: [212.456, 6.972, -59.399, -83.342, 215.038, -97.851]
Example Output: 32.312

Example Input: [-75.664, 192.225, 2.107, -86.22, -51.11]
Example Output: -3.732

Example Input: [70.719, 126.44, 203.395, 115.258, 184.749, 77.713]
Example Output:
129.712