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

namespace lecture
{
    class MainClass
    {

        public 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];
            P[0] = A[0];
            P[1] = A[1];
            for (int i = 0; i < N - 2; i++)
            {
                if(P[i+2] < P[i] + A[i+2])
                {
                    P[i + 2] = P[i] + A[i + 2];
                }

                if (i + 3 < N)
                {
                    if (P[i + 3] < P[i] + A[i + 3])
                    {
                        P[i + 3] = P[i] + A[i + 3];
                    }
                }
              
            }

           // P[i] = Math.Max(P[i - 2] + A[i], P[i - 3] + A[i]);
             
            if (P[N - 2] > P[N - 1])
            {
                Console.WriteLine(P[N - 2]);
            }
            else
            {
                Console.WriteLine(P[N - 1]);
            }
        }
    }
}