Input manager, how to use positive/negative

I see that an entry named "horizontal" has a negative and positive that is A and D.

How can I use this to for example, when user presses A, it will do -1, and when user presses D, it will do 1.

Because if I use if(Input.GetButton("horizontal")) it will only use one value. How do I define what happens if user presses horizontal negative or horizontal positive?

Use GetAxis rather than GetButton.