Thank you Elcius and Malsomnus for the code (mixed you up below, sorry :/) and to everyone else to pointing me into the right direction. That was exactly what I was looking for.
I was so locked into my approach that it just did not came to my mind that taking the average is the solution. Don't ask. Can't believe it myself.
That was one of those situations where I lost the ability to think after unsuccessfully trying to solve a problem for hours.