import sequtils
import strutils
import bitops
import math
import deques

var n = stdin.readLine.parseInt
var a = stdin.readLine.split.map parseInt
var DP = newSeq[int](n+1)

proc get[T](s:seq[T],index :int):T=
    if index < 0 or s.len <= index:
        return 0
    return s[index]

for i in 0..n:
    DP[i] = max(DP.get(i-2)+a.get(i),DP.get(i-1))

echo DP[n]