How to use Running Value when we are using lookupset to retrieve data from other datasets

Hi i have an ssrs reportWhere i have to calculate YTDi used below expression to retrieve data from other datasets using lookupset=Join(LookupSet(Fields!Fin_Indicator_Desc.Value,Fields!Fin_Indicator_Desc.Value,Code.FormattedString(Fields!Resource_Count.Value),"DataSet_ResourceCount"),Constants.vbCrLf)and i want embeed the below expressionto calculate YTD in above expressionIIF(InScope("Month_Name1"),RunningValue(Fields!Resource_Count.Value, Sum, "Fin_Indicator_Desc6"),0)can any please suggest me how to place this Running value expression in above lookupset expression so that i can achieve my target....