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: [-21.77, 172.703, -31.807, 129.587, 84.624, 14.279]
Example Output: 57.936

Example Input: [124.333, 5.477, -53.787, 226.538, -40.577, -43.102, 214.118, 125.785, 151.837]
Example Output: 78.958

Example Input: [191.966, 151.181, -27.921, -97.851]
Example Output:
54.344