# -*- coding: utf-8 -*-
"""
No.45 回転寿司
https://yukicoder.me/problems/no/45

"""
import sys
from sys import stdin
input = stdin.readline


def solve(osushi):
    # 1枚目
    next_OK = 0                 #  今回の皿をパスして、次の皿を取れる状態にした時の美味しさの最大値
    next_NG = osushi[0]         #  今回の皿を取った時の美味しさの最大値
 
    # 2枚目以降
    for o in osushi[1:]:
        tmp = next_NG
        next_NG = next_OK + o
        next_OK = max(tmp, next_OK)

    return max(next_OK, next_NG)



def main(args):
    N = int(input())
    osushi = [int(x) for x in input().split()]
    ans = solve(osushi)
    print(ans)


if __name__ == '__main__':
    main(sys.argv[1:])