Well, in fact, the original title is A Princess of Mars by Edgar Rice Burroughs, first published in book form in 1917 (but previously published in All Story magazine in 1912). This is the book that the film John Carter is based on. The links below are to copyright free editions provided by Project Gutenberg.
HTML version: http://www.gutenberg.org/files/62/62-h/62-h.htm
Kindle version: http://www.gutenberg.org/ebooks/62.kindle.images
Epub version: http://www.gutenberg.org/ebooks/62.epub.images