import sys



def resolve(in_):
    N = int(next(in_))
    V = tuple(map(int, next(in_).split()))

    dp = [[0, 0] for _ in range(N + 1)]

    for i, v in enumerate(V, 1):
        dp[i][0] = max(dp[i - 1])
        dp[i][1] = dp[i - 1][0] + v

    return max(dp[N])


def main():
    ans = resolve(sys.stdin.buffer)
    print(ans)


if __name__ == '__main__':
    main()