如何使用FBFriendPickerViewController设置最大数量的朋友？

I've been working with Facebook to make a multiplayer game. I want to allow the player to be able to invite his friends from Facebook to play in a match, so I use FBFriendPickerViewController for this. However, I want to limit the number of selected friends to a minimun of 1 player and a maximun of 4. I've been working with Facebook to make a multi