Incorrect number count of books on the shelf

[kmnyn]

Error description:
When adding a new book, the message printing "Now you have books on the Shelf: <shelf_name>" is giving wrong number records. The difference is by 3.

Steps to reproduce:

1. Add in a new book using add book command.
   add Dune / Frank Herbert / scifi
2. Expected output:
   I've added: "Dune" by Frank Herbert (Genre: scifi, ID: SCIF-0-0).
   Total books in library: 1
   Now you have 1 books on the Shelf: SCIF-0
3. Actual output:
   I've added: "Dune" by Frank Herbert (Genre: scifi, ID: SCIF-0-0).
   Total books in library: 1
   Now you have -2 books on the Shelf: SCIF-0