The good news: you can get a free burger at Shake Shack today. The bad news: you’ll have to get there quickly because they’re only offering the freebies to the first 100 customers at each location.

The giveaway starts at 10:30 a.m. local time at participating restaurants, the company announced, with free ShackBurgers “or a burger of equal or lesser value” going to customers who get there quickly. The offer doesn’t apply to restaurants in stadiums and ballparks and will only last until noon.

Shake Shack isn’t doing this just because it’s in the mood — the company is celebrating the opening of its 100th restaurant — a new Boston Seaport location — after starting with just one location in New York City’s Madison Square Park in 2004.

“From our first-ever Shack in Madison Square Park twelve years ago, to so many incredible places in between, opening our 100th Shack at Boston Seaport is an epic milestone for us,” said Shake Shack CEO Randy Garutti. “We’re overwhelmed by the love and enthusiasm from our fans around the world, and this moment wouldn’t be possible without them.”

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