As in years past, chairman and CEO Warren Buffett is offering $1 million every year for life to any of his employees who can pick a perfect NCAA tournament bracket through the Sweet 16. This year, the March Madness stakes are even better: Buffett said he’ll double the prize if a team from his home state of Nebraska takes the title.

For Buffett, it’s a pretty safe bet. Of the 18.8 million brackets filled out on ESPN last year, only 18 got the Sweet 16 right. In the four years Buffett has run similar contests, no one has taken home the grand prize.

Here’s what’s happened in the previous contests:

2014

The first year the prize was offered, the contest was open to the public and sponsored by Berkshire Hathaway and Quicken Loans. The prize that year was $1 billion for a perfect bracket, which no one won. A lawsuit later revealed that Yahoo had backed out of a contract to offer a similar contest.

2015

The legal issues that followed the initial 2014 contest meant the contest didn’t happen that year, much to the disappointment of fans who had taken Buffet at his word that he wanted the contest to be easier to win in 2015.

2016

In 2016, Buffett brought the contest back, but just for the more than 300,000 people who work for Berkshire Hathaway and its subsidiaries. Buffett offered $1 million every year for life rather than a one-time payment of $1 billion to anyone who picked a perfect Sweet 16, or $100,000 to the longest surviving bracket. Two Berkshire employees, Kevin Wills of insurance company USLI and Robert Keller of Berkshire-owned Geico, split the $100,000, having each correctly predicted the first 15 games of the tournament.

2017

Last year, the offer was the same: $1 million every year for life for a perfect bracket, or $100,000 for the best bracket. A West Virginia steel worker named Dwayne Johnson came tantalizingly close to winning the grand prize, correctly predicting 31 out of the first 32 games. He won the $100,000 prize for having the bracket that stayed intact the longest.