use std::io;

fn main() {
    io::stdin().read_line(&mut String::new()).ok();
    let mut vv = String::new();
    io::stdin().read_line(&mut vv).ok();
    let vv = vv
        .split_whitespace()
        .map(|n| n.parse::<u64>().unwrap())
        .collect::<Vec<_>>();

    let (mut inc, mut exc) = (0, 0);
    for v in vv {
        let tmp = inc;
        inc = exc + v;
        exc = tmp.max(exc);
    }

    println!("{}", inc.max(exc));
}