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: [245.2, 202.565]
Example Output: 223.882

Example Input: [-6.992, -36.177, -95.203, 87.142]
Example Output: -12.808

Example Input: [165.49, 243.332, 79.089, -56.46, 184.586, 191.468, 80.397]
Example Output:
126.843