import strutils, sequtils

let
  N = stdin.readLine.parseInt
  V = stdin.readLine.split.map parseInt

var
  dp = newSeq[int](N)

block main:
  dp[0] = V[0]
  if N == 1: break

  dp[1] = max(V[0], V[1])
  if N == 2: break

  for i in 2 ..< N:
    dp[i] = max(dp[i - 1], dp[i - 2] + V[i])


echo dp.max