(CNN) — Frontier Airlines is offering free flights for people with the last name “Green” or “Greene.”

The Colorado airline says it operates “America’s greenest flight” and is giving away flights — up to $400 in value — for the promotion of Green Week, the company’s ecofriendly initiative.

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“Our fleet’s fuel efficiency is unmatched by other U.S. airlines and allows Frontier to deliver not only the lowest fares but the most sustainable approach to flying,” President and CEO Barry Biffle said in a statement.

The airline says customer response has been positive.

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“We’re very excited to share our green message with everyone,” said Zach Kramer, a Frontier Airline spokesman, adding that many people are tagging friends with those names. “I was surprised how many people have the last name Green.”

Passengers must book a flight on FlyFrontier.com, must depart on Tuesday and return by August 20, and must legally have the last name Green or Greene.

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