Reverse Variable values depending on third factor

Hello,

I am new to Mathcad. I am using MATHCAD 5.0.0.0. I am trying to define a very simple function described below. Any help will be really appreciated.

Say x=2, y=3

if z=4

x=x and y=y

else 

x=y and y=x

I tried defining a third variable. But was not able to do it inside if statement.

Thanks