from collections import defaultdict, deque, Counter
from heapq import heappop, heappush
from bisect import bisect_left, bisect_right
# 0~9を並び替えるならpermutationsかconbinations,N列のカテゴリを作るにはproduct
from itertools import product, permutations, combinations, accumulate
from functools import lru_cache  # @lru_cache(maxsize=128)
import operator
from string import ascii_uppercase, ascii_lowercase, digits  # 英字(大文字), 英字(小文字), 数字
MOD = 998244353
def II(): return int(input())
def LI(): return list(input())
def LMI(): return list(map(int, input().split()))
def LMS(): return list(map(str, input().split()))
def LLMI(x): return [list(map(int, input().split())) for _ in range(x)]
def LLMS(x): return [list(input()) for _ in range(x)]
  
def execute():
    n = II()
    v = LMI()

    dp = [[-float('INF')] * 2 for _  in range(n+1)]
    dp[0][0] = 0

    # 0はとっていない、1はとっている
    for i in range(1, n+1):
        for j in range(2):
            if j == 0:
                dp[i][j] = max(dp[i-1][j], dp[i-1][j^1])
            else:
                dp[i][j] = dp[i-1][j^1] + v[i - 1]
        
    print(max(dp[-1]))

if __name__ == "__main__":
    T = 1
    for _ in range(T):
        execute()