Android Activity Flow FLAG_ACTIVITY_CLEAR_TOP

Android Activity Flow FLAG_ACTIVITY_CLEAR_TOP

If I have an Activity A starting Activity B which starts a different
instance of Activity A, I would like to go back to the previous Activity A
(the first one in the back stack), and so I've tried using the intent flag
FLAG_ACTIVITY_CLEAR_TOP, but of course this recognizes the top activity as
the running instance rather than the first one. How do I get rid of the
second instance of Activity A & Activity B to resume my session back to
the first Activity A?
A - > B - > A - > Go back to first A and finish second A & B.