Many to Many MDX - Performance

Hi everyone,
I have de following mdx query, it give the result what I need, but without good performance. The dimension "Entidades" is a many-to-many dimension.
How can get the same result writing the query in a different way?

Thanks in advance! :)

WITH
MEMBER [Entidades].[Cod Entidad].MDEntExcluir as
AGGREGATE({[Entidades].[Cod Entidad].&[17]},[Measures].[I CUIT])
MEMBER [Entidades].[Cod Entidad].MDEntidades as
'[Entidades].[Cod Entidad].[ALL] - [Entidades].[Cod Entidad].MDEntExcluir'
SELECT
{[Measures].[I CUIT]} on 0
from [Cubo MKT]
WHERE (
{[Entidades].[Cod Entidad].MDEntidades}
)