use std::{
    collections::{BTreeSet, HashMap},
    hash::Hash,
};

fn main() {
    proconio::input! {
        n: usize,
        v: [i64; n],
    }
    let mut a = vec![0, v[0]];
    for v in v.into_iter().skip(1) {
        a.push(std::cmp::max(a[a.len() - 1], a[a.len() - 2] + v));
    }
    println!("{}", a[a.len() - 1]);
}