using System;
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];
            if (N > 2)
            {
                P[2] = P[0] + A[2];
            }

            for (int i = 3; i < N; i++)
            {
                P[i] = Math.Max(P[i-2],P[i-3]) + A[i];
            }


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