Question: What is the name of the first book in the series that precedes The Heroes of Olympus?

full_context: Document 1: The Last Olympian: The Last Olympian is a fantasy-adventure novel based on Greek mythology by Rick Riordan, published on May 5, 2009. It is the fifth and final novel of the "Percy Jackson & the Olympians" series and serves as the direct sequel to "The Battle of the Labyrinth". "The Last Olympian" revolves around the demigod Percy Jackson as he leads his friends in a last stand to protect Mount Olympus. The title refers to Hestia, the goddess of the hearth, who refers to herself as such in a conversation with Percy on Mount Olympus.
Document 2: Percy Jackson's Greek Gods: Percy Jackson's Greek Gods is a collection of short stories about Greek mythology as narrated by Percy Jackson. It was written by Rick Riordan and was released on August 19, 2014. It features Percy Jackson giving his own take on the Greek myths in a humorous way.
Document 3: The Blood of Olympus: The Blood of Olympus is a young adult novel written by American author Rick Riordan and is the fifth and final book in "The Heroes of Olympus" series. It was released on October 7, 2014. The seven demigods of the Prophecy of Seven—Percy Jackson, Annabeth Chase, Jason Grace, Leo Valdez, Piper McLean, Hazel Levesque, and Frank Zhang—go on their final adventure to defeat Gaea while Nico di Angelo, Reyna Avila Ramírez-Arellano, and Coach Gleeson Hedge attempt to bring the Athena Parthenos to Camp Half-Blood in order to prevent a war between the Roman and Greek demigods. The chapters are written from the perspectives of Jason, Piper, Leo, Reyna, and Nico, making it the first time in the series that someone other than one of the seven demigods of the prophecy is the viewpoint character. It is the second time that Percy appears without being a viewpoint character (first being in "The Lost Hero").
Document 4: The Trials of Apollo: The Trials of Apollo is a series of fantasy adventure mythological fiction novels written by American author Rick Riordan that collectively form a sequel to the "Heroes of Olympus" series. The first book in the series, "The Hidden Oracle", was released on May 3, 2016. The second book in the series, "The Dark Prophecy", was released on May 2, 2017.
Document 5: Percy Jackson (film series): Percy Jackson & the Olympians (also known as Percy Jackson) is an American feature film series based on the novel series of the same name by the author Rick Riordan. The series is distributed by 20th Century Fox, produced by 1492 Pictures and currently consists of two installments. The first film, "" (2010), was directed by Chris Columbus, and was released on February 12, 2010. The second installment, "" (2013) was originally intended to be released in March 2013 but was instead pushed back to August 7, 2013, and was directed by Thor Freudenthal. The series has grossed nearly $430 million at the worldwide box office.
Document 6: Percy Jackson (disambiguation): Percy Jackson is the title character and narrator of Rick Riordan's "Percy Jackson & the Olympians" series.
Document 7: The Lightning Thief: The Lightning Thief is a 2005 fantasy-adventure novel based on Greek mythology, the first young adult novel written by American author Rick Riordan. It is the first novel in the "Percy Jackson & the Olympians" series, which charts the adventures of modern-day twelve-year-old Percy Jackson as he discovers he is a demigod, the son of a mortal woman and the Greek god Poseidon. Percy and his friends Annabeth Chase and Grover Underwood go on a quest to prevent a war between the gods Zeus, Poseidon, and Hades.
Document 8: Percy Jackson: Perseus "Percy" Jackson is a fictional character, the title character and narrator of Rick Riordan's "Percy Jackson & the Olympians" series. He is also one of seven main protagonists of the sequel series "The Heroes of Olympus", appearing in every book except "The Lost Hero," and appears in the ongoing "Trials of Apollo" series, making him one of the few characters to appear in all three series of the Camp Half-Blood chronicles. He has also been a narrator and protagonist in Riordan's Greco-Roman/Egyptian crossover stories, part of the "Demigods and Magicians" collection. The character serves as the narrator in "Percy Jackson's Greek Gods" and "Percy Jackson's Greek Heroes", also by Rick Riordan.
Document 9: The House of Hades: The House of Hades is a 2013 fantasy novel based on Greek and Roman mythology written by Rick Riordan. It is the fourth book in "The Heroes of Olympus" series, which succeeds the "Percy Jackson & the Olympians" series. It is narrated in third person by the seven demigods of the "Prophecy of Seven". The demigods are continuing on their quest from the end of "The Mark of Athena" to close the Doors of Death and slow the progress of the goddess Gaea's army in the mortal world.
Document 10: The Heroes of Olympus: The Heroes of Olympus is a pentalogy of adventure, mythological fiction and fantasy novels by American author Rick Riordan that collectively form a sequel series to the "Percy Jackson & the Olympians" series. This series details a conflict between Greek and Roman demigods and Gaea, the earth goddess. Riordan introduces Roman mythology into his sequel series as well as several new characters. The first book of the series, "The Lost Hero", was published on October 12, 2010. The final entry in the series, "The Blood of Olympus", was published on October 7, 2014.
Document 11: Percy Jackson &amp; the Olympians: Percy Jackson & the Olympians, often shortened to Percy Jackson, is a pentalogy of adventure and mythological fiction books written by American author Rick Riordan, and the first book series in the Camp Half-Blood Chronicles. Five supplementary books, along with three graphic novels, have also been released. More than 45 million copies of the books have been sold in more than 35 countries.
Document 12: Camp Half-Blood chronicles: Camp Half-Blood Chronicles is a media franchise created by author Rick Riordan, encompassing three five-part novel series, three short-story collections, two myth anthology books, a stand-alone short story, an essay collection, a guide, four graphic novels, two films, a video game, a musical, and other media. Set in the modern world, it focuses on groups of demi-god teenagers, and features many characters from Greek and Roman mythology. The first series, "Percy Jackson & the Olympians", follows the adventures of a teen named Percy Jackson at a summer camp for Greek demigods. The second series, "The Heroes of Olympus", introduces several more lead characters and a second camp for Roman demigods. The third series, "The Trials of Apollo", follows the now-mortal god Apollo, with appearances by many characters from the first and second series.
Document 13: The Lost Hero: The Lost Hero is a 2010 fantasy-adventure novel written by Rick Riordan and is based on Greek and Roman mythology. It is the first book in the series "The Heroes of Olympus", the second series about demigods and Camp Half-Blood. It was preceded by the "Percy Jackson & the Olympians" series, which focused solely on Greek mythology.
Document 14: The Demigod Files: The Demigod Files is a collection of stories by Rick Riordan published on February 10, 2009. It is a companion book to series "Percy Jackson & the Olympians". It contains three short stories, titled "Percy Jackson and the Stolen Chariot", "Percy Jackson and the Bronze Dragon", and "Percy Jackson and the Sword of Hades", as well as a preview of "The Last Olympian". It is set between the fourth and fifth novels, "The Battle of the Labyrinth" and "The Last Olympian".
Document 15: The Kane Chronicles: The Kane Chronicles is a trilogy of adventure and Egyptian mythological fiction books written by American author Rick Riordan. The series is set in the same universe as Riordan's "Percy Jackson & the Olympians", "The Heroes of Olympus", and "Magnus Chase and the Gods of Asgard".
ground_truth: Camp Half-Blood Chronicles