<Tr> <Th> LC Class </Th> <Td> PR6051. D3352 </Td> </Tr> <Tr> <Th> Followed by </Th> <Td> The Restaurant at the End of the Universe </Td> </Tr> <P> The Hitchhiker's Guide to the Galaxy is the first of five books in the Hitchhiker's Guide to the Galaxy comedy science fiction "trilogy" by Douglas Adams (with the sixth written by Eoin Colfer). The novel is an adaptation of the first four parts of Adams' radio series of the same name . The novel was first published in London on 12 October 1979 . It sold 250,000 copies in the first three months . </P> <P> The namesake of the novel is The Hitchhiker's Guide to the Galaxy, a fictional guide book for hitchhikers (inspired by the Hitch - hiker's Guide to Europe) written in the form of an encyclopedia . </P>

How many books in the hitchhiker's guide to the galaxy