I want to select two cubes with mouse and then drag both of them

i want to select two cubes and then drag them both with mouse, both selected cubes moves at the same direction with mouse, i have a script which only drag one cube at the time pls help me private Vector3 screenPoint; private Vector3 offset; // Use this for initialization void Start () {

 }
 
 // Update is called once per frame
 void Update () {
 
 }

 
 void OnMouseDown(){
     screenPoint = Camera.main.WorldToScreenPoint(gameObject.transform.position);
     offset = gameObject.transform.position - Camera.main.ScreenToWorldPoint(new Vector3(Input.mousePosition.x, Input.mousePosition.y, screenPoint.z));
 }
 
 void OnMouseDrag(){
     Vector3 cursorPoint = new Vector3(Input.mousePosition.x, Input.mousePosition.y, screenPoint.z);
     Vector3 cursorPosition = Camera.main.ScreenToWorldPoint(cursorPoint) + offset;
     transform.position = cursorPosition;
 }