Moving camera on mouse drag by a fixed distance each time

Hi, Currently I am working on moving a fixed distance with each mouse drag. For example, pressing and dragging the mouse will only move my camera at a max of say 5 units. The camera should move inversely to the direction of the mouse drag. This is down for the implementation of climbing. But even on dragging, the camera keeps on moving till I stop the button. My basic idea is to make a climbing functionality using mouse drags. I cannot think of anything to restrict the distance at each click. Please help.

Here is the sample code:

   // VARIABLES
     public float panSpeed = .001f;
 
     private Vector3 mouseOrigin;
     private bool isPanning;
 
 
     // Update is called once per frame
     void Update()
     {
 
         if (Input.GetMouseButtonDown(1))
         {
             mouseOrigin = Input.mousePosition;
             //right click was pressed    
             isPanning = true;
         }
 
 
         // cancel on button release
         if (!Input.GetMouseButton(1))
         {
             isPanning = false;
         }
 
         //move camera on X & Y
         if (isPanning)
         {
             Vector3 pos = Camera.main.ScreenToViewportPoint(Input.mousePosition - mouseOrigin);
 
             // update x and y but not z
             Vector3 move = new Vector3(pos.x, pos.y, 0) * panSpeed;
 
             Camera.main.transform.Translate(-move, Space.Self);
         }
     }