use std::io::*;
use std::str::*;
use std::cmp::max;

#[allow(dead_code)]
fn get_line(sl: &mut StdinLock) -> String {
    let mut line = String::new();  
    sl.read_line(&mut line).expect("cannot read line");

    line.trim().to_string()
}

#[allow(dead_code)]
fn cast<T: FromStr>(s: &str) -> T {
    s.parse().ok().expect("cannot cast from str")
}

#[allow(dead_code)]
fn get_vec<T: FromStr>(sl: &mut StdinLock, n: usize) -> Vec<T> {
    (&get_line(sl)).split(' ').map(cast::<T>).take(n).collect()
}

fn run(sl: &mut StdinLock) {
    let n = cast::<usize>(&get_line(sl));
    let vs = get_vec::<i32>(sl, n);

    let mut dp = vec![0; n + 1];
    dp[0] = 0;
    dp[1] = vs[0];

    (2..=n).for_each(|i| {
        dp[i] = max(dp[i - 2] + vs[i - 1], dp[i - 1]);
    });

    println!("{}", dp[n]);
}

fn main() {
    let s = stdin();
    let mut sl = s.lock();
    run(&mut sl);
}