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: [163.378, 63.843, 54.946, -61.486, 218.634, 129.505, 16.536]

83.622