getting maximum x and y values of mouse position

hey. I want to get maximum x and y values of mouse position when the player pressing the mouse key. i got the values of all the x's and y's. but i can't figure out how can i eliminate maximum ones and stock in variables. here's my code:

 void FixedUpdate () {
 
 
 
         if (Input.GetMouseButton (0)) {
             
             Vector3 posa = Camera.main.ScreenToWorldPoint (Input.mousePosition);
 
             float x = posa.x;
             float y = posa.y;
                             
             Debug.Log (x);        
                         Debug.Log (y);
         }
     
     }