[Closed] wire expressions

I have a box , its height is controled by a audio wave file . I then have a dumy object and I have wired its Z movment to the height from the box , but what I would like to do is

if box height is lower than 100 then the dummy Z position = 100 .

so ineffect I want to limit the dumy to go no lower than 100 not matter what the height of the box.

hope someone can help me out here