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.

Example Input: [135.807, 205.755, 191.805]
Example Output: 177.789

Example Input: [84.527, 159.538, -20.208, 42.181, -12.587, -86.549, 131.349, 63.615, 150.304]
Example Output: 56.908

Example Input: [218.135, -94.077, -52.486, 118.654, -23.828]
Example Output:
33.28