No amount probably. I wouldn't even know what to spend it on. I don't have expensive habits, don't particularly enjoy travelling, don't need a larger house, don't want children and I really don't like cars, so most of the stuff people to spend tons of money on is out of the picture. I also don't hate my job, so more money adds nothing to my life, while games still do. I also watch quite a bit of pro dota on the side and having to abandon that as well... it's just too much.
Hmm, maybe I could spend a couple of billions on a green resistance kind of thing. But I wouldn't take the money for myself.