import scala.io.StdIn

object Main extends App {
  val n  = StdIn.readLine().toInt
  val b :Array[Int] = StdIn.readLine().split(" ").map(_.toInt)
  var a :Array[Int] = Array(b.head)
  (0 to b.length - 2).foreach {i =>
    val c = List(b(i), b(i + 1)).min
    a = a :+ c
  }
  a = a :+ b.reverse.head
  print(a.sum)

}
