Adding Values between Two Dates - SSRS Expressions

Hi.

I need you help in writing SSRS Expression which counts the Total Values from Start of Month(Date) and GetDate.

For Example:

=SUM(
IIF(Fields!rpt_date.Value = Parameters!RptDate.Value
And Fields!Mot.Value
Like "*In*", Fields!Total.Value, 0), "CoMethod"
)

I want that Fields!Total.Value to be the Start of Month(Date) and Parameters!RptDate.Value

Thanks.Ar

Any Suggestion Experts!