use std::io::Read;

fn main() {
    let mut s = String::new();
    std::io::stdin().read_to_string(&mut s).unwrap();
    let mut splits = s.trim().split_whitespace();
    let n = splits.next().unwrap().parse::<usize>().unwrap();

    let mut ak: Vec<usize> = Vec::new();
    for _ in 0..n {
        ak.push(splits.next().unwrap().parse::<usize>().unwrap());
    }
    //debug!(n, v);
    let mut dp: [usize; 1000] = [0; 1000];

    if n==1 { println!("{}", ak[0]);return; }

    dp[0] = ak[0];
    dp[1] = std::cmp::max(ak[1], ak[0]);
    for i in 2..n {
        dp[i] = std::cmp::max(dp[i-1], dp[i-2]+ak[i]);
    }
    println!{"{}", dp[n-1]};
}