Answer:
The sum does not exist, but if you are in a senior math class, it could be - infinity.
Explanation:
If the sum does not have an endpoint (and it looks like it does not), then the sum really does not exist.
Consider this question.
Does the sum stop at 0 as in
50 + 40 + 32 + 24 + 16 + 8 + 0
But why not - 8 or - 16 or ...
So it is not that the sum does not exit. It is that we do not know where that stop is. Depending on your grade level, you could answer - infinity, but I doubt that is the expected answer.