import scala.io.StdIn

object Main extends App {
  def proc(n: Int, v: Array[Int]): Int = {
    val dp: Array[Array[Int]] = Array.fill(n + 3, 2)(0)

    (0 until n) foreach { i =>
      dp(i + 1)(1) = (dp(i)(0) + v(i)) max dp(i)(1)
      dp(i + 2)(0) = dp(i)(0) + v(i) max dp(i + 2)(0)
      dp(i + 3)(0) = dp(i)(0) + v(i)
    }

    dp(n).max
  }

  val n: Int = StdIn.readInt()
  val v: Array[Int] = StdIn.readLine().split(" ").map(_.toInt)

  val result: Int = proc(n, v)
  println(result)
}