Automatic serial number

I have a sheet with Sl. No. (Col. A) Description(Col. B) and Rate(Col. C). I have included a “flag” field where I will enter “m” for main item and “s” for sub-item. The Sl. No. field is automatically populated based on entry in flag field. (see the attached image)

I have used the formula for Col. A

=IF(D3="s", INDEX($A:$A, ROW()-1)+0.01, 1+ROUNDDOWN(INDEX($A:$A, ROW()-1), 0))

The issue I am facing is that if there is a blank cell above a certain Sl. No., the formula the Sl. No. For the next item is not automatically returned. e.g. If A5 = 1.02 and A6 is blank, then A7 does not automatically populate the serial number based on the flag “s” or “m” in the flag field.
How is the formula to be tweaked to achieve that the blank cells above a certain Sl. No. is ignored and the first instance of the number above Sl. No. field is considered and incremented as per the flag.


Attachment 559646

Thanks,
This works as desired.