Rectangular grid, inversing the Sx and Sy through one slider

Hey guys,

I have created a rectangular grid on grasshopper, which by default has Sx(size of grid cells in x-direction) and Sy(size of grid cells in y-direction). I have added a number slider and connected it to the Sx and Sy. As a result, as Sx increases, Sy also increases. What I am trying to figure out is the following: How can I let  Sx increases as Sy decreases through using one slider? In other words, they are doing the opposite simultaneously.