from itertools import *
from bisect import *
#from math import *
from collections import *
from heapq import *
from random import *
from decimal import *
import numpy as np
import sys

sys.setrecursionlimit(10 ** 6)
int1 = lambda x: int(x) - 1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.readline())
def MI(): return map(int, sys.stdin.readline().split())
def MI1(): return map(int1, sys.stdin.readline().split())
def MF(): return map(float, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LF(): return list(map(float, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
dij = [(1, 0), (0, 1), (-1, 0), (0, -1)]

def main():
    n=II()
    aa=LI()
    dp=[0]*(n+1)
    for i,a in enumerate(aa):
        if i-2>=0:dp[i+1]=max(dp[i-1],dp[i-2])+a
        elif i-1>=0:dp[i+1]=dp[i-1]+a
        else:dp[i+1]=a
    print(max(dp[n],dp[n-1]))

main()