Adapt CONCATENATE to skip rows

Hi,

I'd like to know how adapt the CONCATENATE function to skip rows when copying the formula down a column. For example I am merging rows 3 & 4 using =CONCATENATE(Sheet1!$C3:$AN3,Sheet1!$C4:$AN4) onto Sheet 2 row 3 but it would be very helpful if I could then merge rows 5 & 6 from sheet 1 on row 4 of sheet 2 automatically.

When I copy the formula down currently sheet 2 cell c4 reads =CONCATENATE(Sheet1!$C4:$AN4,Sheet1!$C5:$AN5)

Any thoughts?