Variable Sync across all clients (Photon)

Hi there, i'm currently in the process of working out how to use photon and i've come into a mental wall that I can't seem to get across.

When a player joins a lobby they are meant to get the current amount of players on the server, and then mean to spawn based on that information and then add 1 to the current count.

 void OnJoinedRoom() {
 //Get current playerCount here
         PhotonNetwork.Instantiate (playerPrefabName, spawnPoints[playerCount].position, spawnPoints[playerCount].rotation, 0);
 //Return the new playerCount here
 
     }
 }

Thanks for any help you may give.

Once i've figured out how to get and pass variables then I should have less problems. Sorry for being dense, just tired and cant work it out.