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: [138.602, 158.458, 241.327, 194.509, 169.45, -56.151]
Example Output: 141.032

Example Input: [217.523, 92.701, -55.65, -89.359, 55.742, 158.634, -31.883, 206.554]
Example Output: 69.283

Example Input: [89.956, 243.814]
Example Output:
166.885