use std::io::{stdin, Read, StdinLock};
use std::str::FromStr;

struct Input {
    n: usize,
    v: Vec<usize>,
}

fn read_input(cin_lock: &mut StdinLock) -> Input {
    let n = next_token(cin_lock);
    let v = (0..n).map(|_| next_token(cin_lock)).collect();
    Input { n, v }
}

fn solve(input: Input) -> usize {
    let mut dp = vec![0; input.n];

    for i in 0..input.n {
        dp[i] = dp[i] + input.v[i];

        for j in i + 2..input.n {
            dp[j] = dp[i].max(dp[j]);
        }
    }

    return dp.into_iter().fold(0, usize::max);
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_solve() {
        assert_eq!(
            solve(Input {
                n: 4,
                v: vec![1, 2, 3, 4]
            }),
            6
        );
        assert_eq!(
            solve(Input {
                n: 4,
                v: vec![5, 4, 4, 9]
            }),
            14
        );
        assert_eq!(
            solve(Input {
                n: 7,
                v: vec![1, 2, 9, 10, 1, 1, 4]
            }),
            16
        );
        assert_eq!(solve(Input { n: 1, v: vec![100] }), 100);
        assert_eq!(
            solve(Input {
                n: 3,
                v: vec![1, 100, 1]
            }),
            100,
        );
    }
}

fn next_token<T: FromStr>(cin_lock: &mut StdinLock) -> T {
    cin_lock
        .by_ref()
        .bytes()
        .map(|c| c.unwrap() as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect::<String>()
        .parse::<T>()
        .ok()
        .unwrap()
}

fn main() {
    let cin = stdin();
    let mut cin_lock = cin.lock();
    let input = read_input(&mut cin_lock);

    println!("{}", solve(input));
}