using System;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace lecture
{
    class Program
    {
        static void Main(string[] args)
        {
            int N = int.Parse(Console.ReadLine());

            int[] A = new int[N];
            string[] row = Console.ReadLine().Split();
            for (int i = 0; i < N; i++)
            {
                A[i] = int.Parse(row[i]);
            }
            if (N==1){
                Console.WriteLine(A[0]);
                return;
            }

            int[] P = new int[N + 1];
            P[0] = A[0];
            P[1] = A[1];
            for (int i = 2; i < N + 1;i++){
                P[i] = Math.Max(P[i - 1], P[i - 2] + P[i - 1]);
            }

            if (P[N-2]>P[N-1]){
                Console.WriteLine(P[N - 2]);
            }else{
                Console.WriteLine(P[N - 1]);
            }
        }
    }
}