Unity+FB Graph API- Get friends requests

Could You help me with graph API request?
I would like to get limited list of friends (lets say 5) which are using my game:
This is what i have :

FB.API("me/friends?fields=installed", Facebook.HttpMethod.GET, SomeCallback);	

How/where can I add .limit(5) ?
Thanks !

the code from sample Query user Scores:
FB.API(“/app/scores?fields=score,user.limit(20)”, Facebook.HttpMethod.GET, ScoresCallback);