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?
Use it to hire most of the best minds to be found with the sole purpose of creating an expansive infrastructure to provide regular people the means to organize as one.
The undertaking would be staggering. Reviewing all the known history of man, considering all the languages, cultures, failures and successes.
Researching and combining all known technologies.
All to set the groundwork for a global union of human kind to be able to collectively counteract the disease that is the upper most classes.
After much daydreaming on the subject. I think this is the way of long term existential survival for the human race.
TL;DR: Basically, the Star Trek federation.