title: how to get to the post id of shared story with graph api
body: <p>I get shared story feed with graph api.
  In The result I have fields like :
  type": "photo", 
  "status_type": "shared_story", 
  "object_id": "647332045296931"</p>
  
  <p>the object_id is the photo object.
  I need the post_id of that photo.</p>
  
  <p>How can I get the post id with graph api from that point ?</p>
  
  <p>Thanks</p>