#![allow(unused_imports)]
#![allow(non_snake_case)]
use std::collections::VecDeque;

#[allow(unused_macros)]
macro_rules! read {
    ([$t:ty] ; $n:expr) =>
        ((0..$n).map(|_| read!([$t])).collect::<Vec<_>>());
    ($($t:ty),+ ; $n:expr) =>
        ((0..$n).map(|_| read!($($t),+)).collect::<Vec<_>>());
    ([$t:ty]) =>
        (rl().split_whitespace().map(|w| w.parse().unwrap()).collect::<Vec<$t>>());
    ($t:ty) =>
        (rl().parse::<$t>().unwrap());
    ($($t:ty),*) => {{
        let buf = rl();
        let mut w = buf.split_whitespace();
        ($(w.next().unwrap().parse::<$t>().unwrap()),*)
    }};
}

#[allow(dead_code)]
fn rl() -> String {
    let mut buf = String::new();
    std::io::stdin().read_line(&mut buf).unwrap();
    buf.trim_end().to_owned()
}

trait IteratorExt: Iterator + Sized {
    fn vec(self) -> Vec<Self::Item> {
        self.collect()
    }
}
impl<T: Iterator> IteratorExt for T {}

fn main() {
    let _ = read!(usize; 1);
    let v = read!([usize]);

    let mut table = Vec::<Option<usize>>::with_capacity(v.len());
    for _ in 0..v.len() {
        table.push(None);
    }

    println!("{}", max_score(&v, 0, &mut table));
}

fn max_score(v: &Vec<usize>, i: usize, table: &mut Vec<Option<usize>>) -> usize {
    if v.len() == i {return 0;}
    if i == v.len() -1 {
        table[i] = Some(v[i]);
        return v[i];
    }

    let a = {
        if v.len()-1 < i+2 {
            v[i]
        }
        else {
            if let Some(s) = table[i+2] {
                v[i] + s
            }
            else {
                v[i] + max_score(&v, i+2, table)
            }
        }
    };
    let b = if let Some(s) = table[i+1] {
        s
    }
    else {
        max_score(&v, i+1, table)
    };

    let ans = a.max(b);
    table[i] = Some(ans);
    ans
}