Finding last instance of cell with stock

At first i thought this was a very simple problem, but i seem to have been stuck on this for two days now. See below a list of data. The first column shows the stock level (this will constantly change and is based by formula). The second column is the part number and the third is the order number.

What i need to do is in the 4 column (based on formula) find the last instance of the part number that has stock. if you take part number ZTAR-AT492AV as an example the first two instances have used their stock on that order number, so the third instance which has stock should show the order number in the fourth column, because the third instance still has stock the fourth instance should return a blank (same as 1st and 2nd) in the fourth column, until the stock on the third instance has depleted. When the stock has depleted the third instance fourth column should turn to blank and then the fourth instance fourth column should show the order number.


0 ZTAR-VU895AA 80V026998001(A)
0 ZTAR-VB041AA 80V026998001(B)
0 ZTAR-BP848AA 80V026998001(C)
0 ZTAR-DC369A 80V026998001(D)
0 ZTAR-DT528A 80V026998001(E)
0 ZTAR-AT492AV 80V026998001(F)
0 ZTAR-VD484AV 80V026998001(G)
0 ZTAR-VB841AV 80V026998001(H)
0 ZTAR-AT492AV 80V060249001(A)
15 ZTAR-VS933AV 80V060249001(B)
0 ZTAR-DT528A 80V060249001(C)
7 ZTAR-VB744AV 80V060249001(D)
0 ZTAR-VB841AV 80V060249001(E)
0 ZTAR-VB041AA 80V060249001(F)
0 ZTAR-VU895AA 80V060249001(G)
7 ZTAR-VB043AA 80V060249001(H)
0 ZTAR-DC172B 80V060249001(I)
0 ZTAR-AJ078AA 80V060249001(J)
0 ZTAR-VD484AV 80V060249001(K)
14 ZTAR-AT492AV 80V074929001(A)
10 ZTAR-AP355AA 80V079002001(A)
18 ZTAR-FY943AA 80V079002001(B)
1 ZTAR-VB744AV None
20 ZTAR-VS933AV 80V078973001(A)
0 ZTAR-VD484AV 80V078973001(B)
1 ZTAR-VB043AA 80V078973001(C)
0 ZTAR-DC172B 80V078973001(D)
0 ZTAR-AJ078AA 80V078973001(E)
0 ZTAR-VB041AA 80V078973001(F)
1 ZTAR-VB744AV 80V078973001(G)
0 ZTAR-DT528A 80V078973001(H)
0 ZTAR-VU895AA 80V078973001(I)
65 ZTAR-AT492AV 80V078973001(J)
0 ZTAR-VB841AV 80V078973001(K)
0 ZTAR-DC369A Returns 1A
0 ZTAR-VB041AA Returns 1B
0 ZTAR-DT528A Returns 1C
0 ZTAR-BP848AA Returns 2
6 ZTAR-AT492AV Returns 3A

I haven't put this into a spreadsheet as i thought it would be easier to copy and paste the above, sorry if this breaches any rules.

Any help would be greatly received before i go insane!!
:o)

Iv put this into a spreadsheet please see attachment...

Perhaps this

Hi lian
Find the attached with a helper column and your answer column next to it.