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

#[derive(Debug)]
struct Input {
    n: i32,
    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::<i32>().unwrap())
        .collect();

    Input { n, vs }
}

struct State {
    dp: [u32; 1000],
}

impl State {
    fn new() -> State {
        State { dp: [0; 1000] }
    }

    fn get(&self, i: i32) -> Option<u32> {
        self.as_index(i).map(|i| self.dp[i])
    }

    fn get_or(&self, i: i32, default: u32) -> u32 {
        self.get(i).unwrap_or(default)
    }

    fn set(&mut self, i: i32, value: u32) {
        if let Some(i) = self.as_index(i) {
            self.dp[i] = value;
        }
    }

    fn as_index(&self, i: i32) -> Option<usize> {
        if i >= 0 && (i as usize) < self.dp.len() {
            Some(i as usize)
        } else {
            None
        }
    }
}

fn solve(input: Input, _cin_lock: &mut io::StdinLock) {
    let mut state = State::new();
    for i in 0..input.n {
        let take = state.get_or(i - 2, 0) + input.vs[i as usize] as u32;
        let skip = state.get_or(i - 1, 0);

        state.set(i, cmp::max(take, skip));
    }

    let answer = cmp::max(state.get_or(input.n - 1, 0), state.get_or(input.n, 0));
    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);
}