Definition: 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.
Input: [198.273, -2.503, 217.698, -50.731, -55.456, 158.491, -46.404, -82.953, 68.62]

45.004