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 Vector3 mousePosition = Camera.main.ScreenToWorldPoint(Input.mousePosition);
 Quaternion rot = Quaternion.LookRotation(transform.position - mousePosition, Vector3.forward);
 rot.x = 0.0f;
 rot.y = 0.0f;

 transform.rotation = Quaternion.Slerp(transform.rotation, rot, 1.0f);