use std::cmp;

fn getline() -> String{
    let mut ret = String::new();
    std::io::stdin().read_line(&mut ret).ok();
    return ret;
}

fn getvec(string: String) -> Vec<i32> {
    string.trim().split_whitespace()
        .map(|s| s.parse().unwrap())
        .collect()
}
fn solve(t: i32) -> i32 {
    let v = getvec(getline());
    let mut table = [0; 1000];
    table[0] = v[0];
    table[1] = if t == 1 { 0 } else {v[1]};
    table[2] = if t < 2 { 0 }
    else if table[0]+v[2]>v[1] {table[0]+v[2]}
    else {v[1]};
    for i in 3..t {
        let a = table[(i-1) as usize];
        let b = table[(i-2) as usize]+v[i as usize];
        let c = table[(i-3) as usize]+v[i as usize];
        table[i as usize] = cmp::max(cmp::max(a, b), c);
    }
    return table[(t-1) as usize]
}

fn main() {
    let t:i32 = getline().trim().parse().unwrap();
    println!("{}", solve(t));
}