Copy formula with skipping rows

An easy problem is driving me crazy, may be this is impossible in Excel...

Please have a look at the simple example attached.

In cell D1 I have the formula '=b1'. What I would like to do is the following: I want to drag this formula down, but when I'll do this then cell D3 will contain the value 6, with the formula '=b3'. However cell d3 currently contains the formula '=d1+d2' that is the right formula that I also want to keep.

So, what I would like to do is copying the formula and skipping the rows that are called 'Total'. In addition I face the difficulty (for now ignoring the fact that the rows total should contain another formula) when you copy the formula '=b1' down then in cell D7 the formula will be '=b7', while it should be '=b5'.

Shortly, does someone know an option in Excel to copy a formula down with skipping rows.

Please let me know if I'm not clear. Look forward to your ideas, thanks for your help!