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

namespace ConsoleApplication6
{
    class Program
    {
        public static void Main(string[] args)
        {
            int N = int.Parse(Console.ReadLine());

            int[] A = new int[N];
            int[] B = 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;
            }

            B[0] = A[0];
            B[1] = A[1];

            for (int i = 0; i < N - 2; i++)
            {
                if (i + 2 < N && B[i+2] < B[i] + A[i+2])
                {
                    B[i + 2] = B[i] + A[i + 2];
                }
                if (i + 3 < N && B[i] < B[i] + A[i + 3])
                {
                    B[i + 3] = B[i] + A[i + 3];
                }
            }

                Console.WriteLine(B.Max());
        }
    }
}