use std::io::Read;
use std::cmp;

fn main() {
    let mut buf = String::new();
    std::io::stdin().read_to_string(&mut buf).unwrap();
    let mut iter = buf.split_whitespace();
    
    iter.next();
    let sushi_lane = iter.map(|v| v.parse::<usize>().unwrap());
    
    let mut max_one_before: usize = 0;
    let mut max_two_before: usize = 0;
    
    for sushi in sushi_lane {
        let cur_max: usize = cmp::max(sushi + max_two_before, max_one_before);
        max_two_before = max_one_before;
        max_one_before = cur_max;
    }
    
    println!("{}", max_one_before);
}