I need get the last Id of dimention

I have:Fact:Pk_Fact Id_Dim1 Id_Dim2 Value 17 2 3 15 21 2 2 20 22 2 5 25 23 2 1 35 30 2 4 40Dim1:Id_Dim1 DesDim1 2 'Description 2'Dim2:Id_Dim2 DesDim2 1 'Description 1' 2 'Description 2' 3 'Description 3' 4 'Description 4' 5 'Description 5'I need get the id of the last fact using MDX: Result spected : Sum(Value)=145 Id_Dim1 = 4 --> (*) its posible get this with mdxThanks