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: [-64.31, 66.053, 186.893, 104.617, -19.939, 169.377, -87.888]

50.686