The book is by Rick Riordan. It is book 1 of the "The Heroes of Olympus" series. The paperback has 557 pages.
The Lost hero has 56 chapters and 553 pages or around that
556 pages
Conan the Hero has 278 pages.
Rise of a Hero has 480 pages.
Hero in the Shadows has 406 pages.
Once a Hero - novel - has 400 pages.
Son of a Smaller Hero has 208 pages.
What Was Lost has 240 pages.
A Hero Ain't Nothin' but a Sandwich has 126 pages.
The Lost Stories has 580 pages.
The Lost Slayer has 136 pages.
Lost Face has 240 pages.