Summing Or Adding Up Date Wise Column But No Duplication Of Dates

Problem,

A B C D E F (B+C-D-E)
Date Opening Stock Purchase Sales Consumption Closing Stock
17/7/2012 10000 5000 1000 2000 12000
17/7/2012 12000 2000 2000 1000 11000
18/7/2012 11000 0 1000 5000 5000
18/7/2012 5000 10000 3000 0 12000

Note : I want the above result as shown below datewise but no duplication of date but summing up of column C,D and E which is in above.Pls note that this is accounting question and also plz note that Opening stock(column B) from next date onwards must be equal to previous date closing stock(Column F).

Results :

A B C D E F (B+C-D-E)
Date Opening Stock Purchase Sales Consumption Closing Stock
17/7/2012 10000 7000 3000 3000 11000
18/7/2012 11000 10000 4000 5000 12000
(B=F)

if I could get the formula in excel ,since this is the sample data as I do have a numerous & huge data like shown above datewise where I need to add C ,D and E but Opening stock(column B) from next date onwards must be equal to previous date closing stock(Column F).