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: [89.047, 195.178]
Example Output: 142.112

Example Input: [210.345, 91.115]
Example Output: 150.73

Example Input: [35.682, 21.673, 167.016, 90.953, 229.342, 240.03, -81.506, 244.785, 211.557]
Example Output:
128.837