import scala.io.StdIn

object Main {
  def main(args: Array[String]): Unit = {
    val n = StdIn.readInt
    val v = StdIn.readLine.split(' ').map(_.toInt)

    val dp = Array.fill(n)(0)

    for (i <- (0 until n)) {
      var sushi = v(i)
      if (i - 1 >= 0) sushi = Math.max(sushi, dp(i - 1))
      if (i - 2 >= 0) sushi = Math.max(sushi, dp(i - 2) + v(i))
      dp(i) = Math.max(dp(i), sushi)
    }

    println(dp(n - 1))
  }
}