use std::cmp::max;

fn main() {
    let mut n = String::new();
    std::io::stdin().read_line(&mut n).ok();
    let n: usize = n.trim().parse().unwrap();
    let mut v = String::new();
    std::io::stdin().read_line(&mut v).ok();
    let v: Vec<usize> = v.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();

    if n == 1 {
        println!("{}", v[0]);
        return;
    }
    if n == 2 {
        println!("{}", max(v[0], v[1]));
        return;
    }
    let mut dp: Vec<usize> = vec![0; n];
    dp[0] = v[0];
    dp[1] = v[1];
    dp[2] = v[0] + v[1];
    for i in 3..n {
        dp[i] = max(dp[i-3]+v[i], max(dp[i-2]+v[i], dp[i-1]));
    }
    println!("{}", dp[n-1]);
}