Sheet numbering

[raullg]

I need to solve the following problem:

I want to write in the header of the document the page's number, but with this order:

First and second page --->>> SHEET 1
Third and fourth page ---->>> SHEET 2
Fifth and sixth page ------>>> SHEET 3
and so on


The number of pages is variable, for this reason I need to introduce this numbering in the header.

I think i 'm going to need a macro, because with the WRITER options i am not able to solve the problem.

Anyone can help me with a solution or a macro???