Cumulatively SUM Column While Looping?

I have 4 columns of data, Col A id for pipes, Col B upstream_node_id, Col C downstream_node_id and Col D connected assets. I want to create Col E with the cumulative count of upstream connected assets.

Data looks like this :

A B C D E
Pipe ID U/S Node ID D/S Node ID Nr Connected Assets Nr U/S Connected Assets
78057358 74888997 1026722856 2 39
78057352 74888992 74888997 4 37
78057346 75107198 74888992 6 33
78531653 74888757 75107198 6 27
78057340 74888987 74888757 2 11
78057046 74888762 74888757 6 10
78057334 74888982 74888987 9 9
78057040 74888767 74888762 4 4

See how the D/S Node ID can appear more than once in Col C.

I have added Col E manually to demonstrate the output I am looking for.

I am no expert but I think that this would be something like a nested loop, but the number of nested loops can't be determined before hand ??

I have written out what I think I need to do, but don't really know how to code it :

i. For each Pipe_ID (Col A) get U/S Node ID (Col B) and add to "selection".
ii. For each U/S Node ID (Col B), find all matching U/S Node ID (Col C), and add to selection and get the U/S Node ID (Col B) for those.
iii. Populate Col E with sum of Col D for "selection".
iv. Repeat Until U/S Node ID (Col B) can't be found in U/S Node ID (Col C).

How to get the table to align correctly.