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: [-10.458, 179.095, 14.687, 16.22, -27.798, -77.438, 47.503]

20.259