Total in MDX

Hi, I have a problem when i browse the cube.

I have this MDX calculation: iif(x>y,x,y)

The problem is that the total is not correct. For example:

             calculation

1              5

2              3

3            2

total        12

But if I drop "x" or "y" in the browse each total is corrrect. So I think that there is a problem with the calculation. Can someone help me?

Thanks!!