 The producers each read the book over the course of a single night and agreed the next morning that it was "the most exciting thing that they had ever read" and that they wanted to produce a film version, although they were unsure how it would be accomplished.They purchased the film rights in 1973, before the book's publication, for approximately $175,000 (equivalent to $990,000 in 2018).Brown claimed that had they read the book twice, they would never have made the film because they would have realized how difficult it would be to execute certain sequences.