use std::cmp;
use std::io::{self, Read};

#[derive(Debug)]
struct Input {
    n: usize,
    vs: Vec<i32>,
}

fn next_token(cin_lock: &mut io::StdinLock) -> String {
    cin_lock
        .by_ref()
        .bytes()
        .map(|c| c.unwrap() as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect::<String>()
}

fn read_input(cin_lock: &mut io::StdinLock) -> Input {
    let n = next_token(cin_lock).parse().unwrap();
    let vs = (0..n).map(|_| next_token(cin_lock).parse().unwrap()).collect();
    Input {
        n,
        vs,
    }
}

fn solve(input: Input, _cin_lock: &mut io::StdinLock) {
    let answer = solve_dp(input);
    println!("{}", answer);
}

fn solve_dp(input: Input) -> i32 {
    if input.n <= 2 {
        let first = *input.vs.get(0).unwrap();
        let second = input.vs.get(1).map(|x| *x).unwrap_or(0);
        return cmp::max(first, second);
    }

    let mut dp = vec![0; input.n];
    dp[0] = input.vs[0];
    dp[1] = cmp::max(input.vs[0], input.vs[1]);

    for (i, v) in input.vs.into_iter().enumerate().skip(2) {
        let take = *dp.get(i - 2).unwrap() + v;
        let skip = *dp.get(i - 1).unwrap();
        dp[i] = cmp::max(take, skip);
    }

    let mut it = dp.into_iter().rev();
    cmp::max(it.next().unwrap(), it.next().unwrap())
}

fn main() {
    let cin = io::stdin();
    let mut cin_lock = cin.lock();

    let input = read_input(&mut cin_lock);
    solve(input, &mut cin_lock);
}