"""
Yukicoder No. 45 回転寿司

author: yamaton
date: 2015-12-18
"""

import itertools as it
import functools
import operator
import collections
import math
import sys

def solve(xs, n):
    dp = collections.defaultdict(int)
    for i in range(n):
        dp[i] = max(xs[i] + dp[i-2], dp[i-1])
    return dp[n-1]


def pp(*args, **kwargs):
    return print(*args, file=sys.stderr, **kwargs)


def main():
    n = int(input())
    xs = [int(i) for i in input().split()]
    assert len(xs) == n
    result = solve(xs, n)
    print(result)


if __name__ == '__main__':
    main()