from collections import defaultdict

memo = {}


def dfs(i, pre_use):
    if i == len(value_list):
        return 0

    if (i, pre_use) in memo:
        return memo[(i, pre_use)]

    ans = 0
    ans = max(ans, dfs(i + 1, False))
    if not pre_use:
        ans = max(ans, dfs(i + 1, True) + value_list[i])

    memo[(i, pre_use)] = ans
    return ans


if __name__ == '__main__':
    n = int(input())
    value_list = list(map(int, input().split()))
    print(dfs(0, False))