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: [155.467, -40.717, -24.529, -22.608, 38.752]
Example Output: 21.273

Example Input: [172.084, 126.948, 90.757]
Example Output: 129.93

Example Input: [35.844, 44.846, 32.366]
Example Output:
37.685