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

#[derive(Debug)]
struct Input {
    n: usize,
    vs: Vec<u32>,
}

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 max_value_of(input: Input) -> u32 {
    if input.n == 1 {
        return input.vs[0];
    }

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

    for i in 2..input.n {
        let take = dp[i - 2] + input.vs[i];
        let skip = dp[i - 1];
        dp[i] = cmp::max(take, skip);
    }
    dp[input.n - 1]
}

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

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

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