How do I get a specific coordinate position of a brick? (i.e. Get the Z position specifically.)

game.Players.PlayerAdded:connect(function(player)
	local character = player.Character
	if character.Head.Position >= Vector3.new(0,0,-100) then
		local dostuffhere = dostuffhere
	end
end)

That is my code so far, but I want the script to pay attention only to the Z position. I'll make it do stuff later. Thank you!