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: [139.6, 119.652, 135.338, 171.029, 247.554, 222.19, -61.931, 120.928, 235.688]
Example Output: 147.783

Example Input: [199.974, 2.205, 197.996, 172.426, 182.153, 42.045, 53.238, 18.021, 83.903]
Example Output: 105.773

Example Input: [192.084, 220.115, 26.249]
Example Output:
146.149