Sequentially numbering specific cells

Hello. I'm fairly new to excel and i'd appreciate someones help. I need help with sequentially numbering specific excel cells This link will provide you with the worksheet that i am currently working on http://www.mediafire.com/?twtmtydo4od -- we use this label every single day and if you look at next to " CTN: " on the middle right portion of the label, that is the # of the label. My question is, is there any macro or formula that i can use to sequentially number each label's "CTN " cell automatically? For now we are changing each number manually and as you can tell it takes a lot of time. If anyone can give me any kind of assistance i'd greatly appreciate it.

Thank you so much in advance.

EDIT: Sorry for linking a second party download link. I've attached the file through this post.