How to left click to rotate a box in a same direction in Unity 2D?

I have a project here that want me to make a box rotate 90 degrees when clicked on Unity C#. It need to be rotate in a constant direction which is rotate to right 90 degrees every time i click. Can anyone show me some example how to code it? Thanks.

if (Input.GetMouseButtonDown(0))
{
transform.Rotate(0,90,0);
}