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: [57.157, 114.845, 139.172, -10.388, 41.101, 199.327, -5.868]

76.478