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: [249.671, -12.816, 21.299, 8.341, 141.384, 64.552, 165.886]

91.188