carrying forward

Hi,

I am trying to create a function that would do the following:
you have a maximum claim that you can expense per year(10; column 1), and you have your expenses (column 2). However, if your expenses are greater that the maximum expense for the year, you can carry it forward to the next year and claim in in following years.
Basically I want to set up a function that replicate the claimed column
Hope this make sense

Many thanks for your help

Maximum Expense Expense Claimed
10....................... 7 .............7
10....................... 9 .............9
10 ...................... 12............10
10 ....................... 13............10
10.......................... 2............7
10..........................11............10
10...........................8............9

C2 and down: =MIN(A2, SUM(B$1:B2) - SUM(C$1:C1))

And any idea for C1?

Header row.