[2D Mode] Trying to make a sprite dragable

I have setup 4.3 in 2D mode and I'm trying to simply drag a sprite on click.

I was under the impression the coordinates I need would be from Camera.main.ScreenToWorldPoint(Input.mousePosition) So I have:

 void Update(){

     Debug.Log (Camera.main.ScreenToWorldPoint(Input.mousePosition).ToString());
 
 }

 void OnMouseDown(){
     transform.position = Camera.main.ScreenToWorldPoint(Input.mousePosition);
 }

But this doesn't work, infact the position returned by Camera.main.ScreenToWorldPoint(Input.mousePosition) is always (0.0, 1.0, -10.0) no matter where the mouse is.

Any ideas?

EDIT: Solved it

Screen to world wants a vector3 and technically I was supplying only 2 dimensions, although it ran... You need to separate mouse x and y and then supply z which is the distance of the object from the camera. Also OnMouseDrag is obviously better for drag functionality

New code looks like this:

 public class ButtonClick : MonoBehaviour {
 float x;
 float y;
 
 // Update is called once per frame
 void Update(){
     x = Input.mousePosition.x;
     y = Input.mousePosition.y;
 }

 void OnMouseDrag(){
     transform.position = Camera.main.ScreenToWorldPoint(new Vector3(x,y,10.0f));
 }

}