import java.util.Scanner;

/**
 * Created by whiled on 17/05/04.
 */
public class Main {
    public static void main(String[] args){
        Scanner scan = new Scanner(System.in);
        int N = scan.nextInt();
        int[] v = new int[N];
        for (int i=0; i<N; i++) v[i] = scan.nextInt();

        int[] res = new int[N+1];

        res[0] = 0;
        res[1] = v[0];
        if (res.length > 2) res[2] = Math.max(v[0], v[1]);
        for (int i=2; i<res.length-1; i++){
            res[i+1] = Math.max(res[i], res[i-1] + v[i]);
        }

        System.out.println(res[N]);
    }


}