如何检索我刚刚通过 Facebook API 发布的帖子的帖子 ID

i am using the following code to publish to a Page's feed connection

    $attachment = array('message' => 'xxxxxxxxxxxxxxxxx',
            'name' => 'cccccccccccccccc',
            'caption' => 'cccccccccccccccc',
            'link' => 'http://apps.facebook.com/manydldotnet/',
            'description' => "ccccccccccccc",
            'picture' => "'cccccccccccccccc'",
            'actions' => array(array('name' => 'Download!','link' => 'http://apps.facebook.com/manydldotnet/'))
            );

$result = $facebook->api('/121468571287906/feed/','post',$attachment); 

那么问题是如何在发布后获取post_id?