Running Total

Hi Guys,

Im trying to create a balance sheet using my AS cube. I need to create a running total month on month which i can do by using this:

Sum({
            {[Date].[Calendar].CurrentMember.Level.Members}.Item(0):
            [Date].[Calendar].CurrentMember
        }, [Measures].[Amount])

However, when a new year starts i need the running total to start from 0 again, is there any easy way to do this?

Example

                         2011                                         2012

                          1    2     3    4    5    6    etc       1     2     3

Account Group   5    10  25   30  55   66               6    10   88

Cheers

Dave