4 books
The Road to Oz
The Emerald City of Oz
The Road to Oz; In Which Is Related How Dorothy Gale of Kansas, the Shaggy Man, Button Bright, and Polychrome the Rainbow's Daughter Met on an Enchanted Road and Followed It All the Way to the Marvelous Land of Oz
The Marvelous Land of Oz; Being an Account of the Further Adventures of the Scarecrow and Tin Woodman ... a Sequel to the Wizard of Oz