Checking the number of Pokemon in the player's party

I want a NPC that only let me pass if I have a maximum of 3 Pokemon in my Team. I need the right Conditionak Branch or Variables, if there's one.

Put this in a conditional branch (script option)
$Trainer.ablePokemonCount>3
That will count unfainted pokemon, for unfainted and fainted use
$Trainer.pokemonCount>3

This stuff is all on the wiki, not hard to find.