13

object maguc {
  def f(n:Int,A:String,C:String,B:String):Unit ={
    if(n == 1){
      println(s"${A} →${C}")
    } else {
      f(n-1,A,B,C)
      println(s"${A} →${C}")
      f(n-1,A,B,C)
    }
  }
  def main(args:Array[String]):Unit={
    f(5,"A","B","C")
  }

}