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: [20.538, 100.835, -23.197, 207.707, -12.758, 152.97, 190.404]
Example Output: 90.928

Example Input: [102.524, 88.129, 196.972]
Example Output: 129.208

Example Input: [-67.456, 19.727, 170.816, 47.046, -34.967, 114.317, -66.564]
Example Output:
26.131