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: [243.593, 73.842, 233.891, 207.996, 9.099, -15.81, 236.911, 152.289, -3.803]

126.445