function Main(input) {
  function rec(v, i) {
    if (N <= i) {
      if (max < v) max = v
      return
    } else {
      rec(v, i + 1)
      v += values[i]
      rec(v, i + 2)
    }
  }
  const data = input.trim().split("\n")
  const N = parseInt(data[0])
  const values = data[1].split(" ").map(v => parseInt(v))
  let max = values[0]
  rec(0, 0)
  console.log(max)
}
Main(require("fs").readFileSync("/dev/stdin", "utf8"))