#region Header
#!/usr/bin/env python3
# from typing import *

import sys
import io
import math
import collections
import decimal
import itertools
from queue import PriorityQueue
import bisect
import heapq

def input():
    return sys.stdin.readline()[:-1]

sys.setrecursionlimit(1000000)
#endregion

# _INPUT = """# paste here...
# """
# sys.stdin = io.StringIO(_INPUT)


def main():
    N = int(input())
    V = list(map(int, input().split()))

    dp = [0 for _ in range(N+1)]
    dp[0] = 0
    dp[1] = V[0]
    for i in range(2, N+1):
        dp[i] = max(dp[i-2] + V[i-1], dp[i-1])
    print(dp[N])


if __name__ == '__main__':
    main()