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: [-42.207, -46.667, 171.095]
Example Output: 27.407

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

Example Input: [89.53, 164.022, 246.192, -98.857, -61.39, -32.699, 120.685, 121.712]
Example Output:
68.649

