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: [173.903, 103.626, -96.508, 63.59, 44.234, -81.913, 189.138]

56.581