you can try this formula in cell E2 and copy it down the column:
=IF(IF(ISERROR(VLOOKUP(C2,Stock!$A$2:$B$12,2,FALSE)),0,IF(VLOOKUP(C2,Stock!$A$2:$B$12,2,FALSE)-SUMIF($C$1:$C1,$C$2,$D$1:$D1)>D2,D2,VLOOKUP(C2,Stock!$A$2:$B$12,2,FALSE)-SUMIF($C$1:$C1,$C$2,$D$1:$D1)))<0,0,IF(ISERROR(VLOOKUP(C2,Stock!$A$2:$B$12,2,FALSE)),0,IF(VLOOKUP(C2,Stock!$A$2:$B$12,2,FALSE)-SUMIF($C$1:$C1,$C$2,$D$1:$D1)>D2,D2,VLOOKUP(C2,Stock!$A$2:$B$12,2,FALSE)-SUMIF($C$1:$C1,$C$2,$D$1:$D1))))