object Main extends App {
  val sc = new java.util.Scanner(System.in)
  val n = sc.nextInt
  val p = Array.fill(2 * n)(sc.nextLong).sorted
  val e = p.zipWithIndex.filter(_._2 % 2 == 0).map(_._1)
  val o = p.zipWithIndex.filter(_._2 % 2 == 1).map(_._1)
  val ans = e.zip(o).map(p => p._1 * p._2).sum
  println(ans)
}