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: [138.526, 60.81, 233.845, -33.602, 189.784, 13.888, 184.543, 53.635, 18.299, -87.132]

77.26