import scala.io.StdIn._
object Main extends App {
  val n = readInt
  val expression = readLine.trim.split('+')
  val count = ('a' to 'z').map{c ⇒ expression.count{_.head == c}}.toArray
  println(
    if (n == 1) 1 else (1 to 9).map{size ⇒ count.count{_ == size}.let{term ⇒ if (term == 0) 0 else if (size == 1) term else if (term == 1) 3 else term + 4}}.sum + count.count{_ != 0} - 1
  )
  implicit class Extension[T](val value: T) extends AnyVal {
    @inline def let[A](@inline func: T ⇒ A): A = func(value)
    @inline def also(@inline func: T ⇒ Unit): T = {func(value); value}
  }
}
