How to sum (SUMIF OR SUMIFS) only when there are consecutively same values?

I have a condition column where some "condition values" are consecutive, which may or may not repeat further down, while some are single "condition values". I need to sum (either using SUMIF or SUMIFS) only those values whose "condition values" are consecutive. For example,

Note the sum of A's after D's starts with 0 and adds only the three consecutive A's.

You don't need SUMIF for this, the formula can be defined like this:

• If Condition on current row != Condition on the previous row, Sum for this row = Value for this row
• Else, Sum for this row = Sum for previous row + Value for this row. This will take care of the "consecutive" aspect.

Assuming the above data starts at A1:

# Cell D2
=IF(A2<>A1,B2,B2+D1)