Auto number rows

Hi all

Please I need your help with a vba code to autonumber cells in excel.

My data will be contained on column C to G and the autonumber will be in column B, however some rows in column C will be merged across multiple rows but they still need to be numbered as 1 row.

I will also have some rows merged horizontally across column B to G, these should not be numbered.
For example ( see attached image)
Attachment 25420

I will like to be able to update the number from a specific row when a new row is inserted or deleted.

Thanks for your help.

Ola