Turn camera with mouse

Hi. I got a small problem. I want to rotate my camera with mouse (Mouse X axis) . With joystick its easy because the Input.GetAxis doesn't return 0 while you pull the analog stick. But in mouse it's different because when you finish your drag movement, its returning 0. What i want to do is rotate camera as long as the mouse is on right edge or left edge. Anyone have an idea about it?

 

Btw, if you get the mouse as an axis, it will still give you values even if the actual cursor doesn't move.
But basically the code would look like this:

Code (CSharp):

1. if (Input.mousePosition.x < someThreshold) {
2.     rotate here
3. }

And similarly for the other 3 edges

 

thanks for your reply yeah i'm using a threshold value i meant aproximetly 0