Your final page count must be an even number (divisible by 2).
Final page count includes all pages that comprise the interior of a book, numbered & non-numbered, including front matter and back matter such as: Table of Contents, Acknowledgements, Copyright page, photo inserts, Appendices, etc. The last page in the book, facing the inside back cover, must be blank for Lightning Source's bar code and is included in the final page count. The final page count will also include any blank pages LS must add. The final page count determines the print cost for the interior of the book.
Why is the correct page count important to your book? The width of the cover spine is directly dependent upon the number of pages in the interior. The front and back matter can encompass numerous pages. If front and back matter are not considered in the page count, the cover file will have an incorrect spine width and may cause your project to be delayed.