import scala.annotation.tailrec
import scala.io.StdIn

object Problem205 {

  def proc(N: Int, S: Seq[String]): String = {
    @tailrec
    def rec(result: Seq[Char], S: Seq[String]): String = {
      if (S.isEmpty) return result.reverse.mkString("")

      val sorted = S.sorted
      val (next, others) = (sorted.head, sorted.tail)
      val nextChar: Char = next.head

      val remains: Seq[String] = next.tail match {
        case "" => others
        case x if x.startsWith("{") => others
        case x => (x + "{") +: others
      }

      rec(nextChar +: result, remains)
    }

    val padS = S.map(s => s + ("{" * (N - s.length)))
    rec(Nil, padS)
  }

  def main(args: Array[String]) = {
    val N = StdIn.readInt()
    val S = Seq.fill(N)(StdIn.readLine())
    val result: String = proc(N, S)
    println(result)
  }
}