How do I testfor a certain amount of players in a certain radius?

So I am making a Spleef game on my server and I need to testfor 12 players within about 35 blocks from the command blocks.

I tried /testfor @a[r=35] leading into a /tp command to teleport the players into the Spleef arena. What I don't have is to make it only teleport 12 players and not any more or less. So if you can help me with this I'd appreciate it.

Solution 1:

There is the count target selector argument.

/tp @p[x=<X>,y=<Y>,z=<Z>,r=<Radius>,c=<Count>] x y z

To detect if there is 12 players or more, there are 2 main ways to do it. One is simply with a comparator leading from a /testfor @a[x=<X>,y=<Y>,z=<Z>,r=<Radius>], which will emmit a redstone signal strength equal to the amount of players in that area and you can run a redstone wire to activate the teleport command, or do it with a scoreboard counter.