import java.io.{BufferedReader, InputStreamReader}

object Main {
  def main(args: Array[String]): Unit = {
    val in = new BufferedReader(new InputStreamReader(System.in))
    val _ = in.readLine().toInt
    val bs = in.readLine().split("\\s+").map(_.toInt)

    System.out.println(
      bs.head + bs.zip(bs.tail).map {
        case (b1, b2) => Math.min(b1, b2)
      }.sum + bs.last
    )
  }
}
