function Main(input) {
  const data = input.trim().split("\n")
  const N = parseInt(data[0])
  const values = data[1].split(" ").map(v => parseInt(v))
  let checked = Array.apply(null, Array(N)).map(() => -1)
  checked[0] = values[0]
  if (N === 1) {
    console.log(checked[0])
    return
  }
  checked[1] = values[1]
  for (let i = 1; i < N - 1; i++) {
    checked[i + 1] = Math.max(checked[i], checked[i - 1] + values[i + 1])
  }
  console.log(checked[N - 1])
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"))