First,  before I took the money,  I would talk to a tax guy.    How to maximize the benefit.   

For example,   assume they take half in taxes.   If I gave half away to charity  ($2.9 million)   they could not tax me on that.   I would have $2.9 million left.   They WOULD tax me on that,  leaving me $1.45 million.   So by me giving up $1.45 million,  I could benefit charity by $2.9 million.   Seems to me a fair trade.  

Since $1.45 million is more than I could ever imagine getting,  the joy of giving $2.9 million to charity would be worth doing.