use proconio::*;
fn main(){
    input!{
        n: usize,
        a: [usize; n]
    }
    let mut p0=0;
    let mut p1=a[0];
    for i in 1..n{
        let curr=p1.max(p0+a[i]);
        p0=p1;
        p1=curr;
    }
    println!("{}", p1);
}