What is the most amount of money you would be willing to pay for an extra year of life?

You can, at any point, pay to extend your life for a year. There is no limit on the number of extra years you can pay for. Also, the offer is exclusive to you meaning that billionaires don't get to live forever.

The amount you choose is also how much you'd have to pay for every other year that you choose to buy.

To clarify, I'm asking you what is the greatest sum of money you'd be willing to part with, if it means living a year longer.