It has no "answer".
If the terms are arranged as: 1 + (1 - 1) + (1 - 1) + (1 - 1) + ...
then the answer will be 1 + 0 + 0 + 0 + ... = 1.
However, if the terms are arranged as: 1 + 1 + (-1 + 1) + (-1 + 1) + (-1 + 1) + ...
then the answer will b2 2 + 0 + 0 + 0 + ... = 2.
So, there is no single "answer".
(You might like to see if you can rearrange the terms to get other answers ...)