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: [231.159, 217.795, 230.676, -11.951, -82.697, 31.413]
Example Output: 102.732

Example Input: [220.903, 155.959]
Example Output: 188.431

Example Input: [98.331, 146.867, -44.972, 175.209, 154.846, -33.41, 110.339, 229.773, 103.873]
Example Output:
104.54