You get to keep only enough to maintain a very modest lifestyle in a low-cost-of-living area, the rest of it has to go towards improving the world in some way.
Edit: Given the previous rules that you must maintain a very modest lifestyle in a low-cost-of-living area, would you rather choose to opt out and not have the money at all?
I wouldn’t even know where to begin. I’d rather just opt out and keep living my current lifestyle than dedicate the rest of my life to something I’m not an expert in - and honestly, don’t even find particularly interesting.
That is very fair.