import sequtils,strutils,strscans,algorithm,math,future,macros
template get*():string = stdin.readLine() #.strip()


let
  N = get().parseInt()
  V = get().split().map(parseInt)

# 連続では取れない
var
  ok_do = 0
  ok_dont = 0
  no_dont = 0
for i,v in V:
  (no_dont,
   ok_do,
   ok_dont) = (
     ok_do + v,
     max(ok_dont,no_dont),
     max(ok_dont,no_dont))
echo max(@[ok_do,ok_dont,no_dont])