using System;
using System.Collections.Generic;
using System.Linq;

namespace yukicoder
{
    public class Program
    {
        public static void Main()
        {
            var n = int.Parse(Console.ReadLine());
            var v = new int[n];
            var vsum = new int[n];
            var line = Console.ReadLine().Split(' ');
            for (var i = 0; i < n; i++)
            {
                v[i] = int.Parse(line[i]);
            }
            if(n == 1){
                Console.WriteLine(v[0]);
            }
            else{
                var x = new Queue<int>();
                x.Enqueue(0);
                x.Enqueue(1);
                while (x.Count > 0)
                {
                    var k = x.Dequeue();
                    if (k + 2 < n && vsum[k] + v[k] > vsum[k + 2])
                    {
                        vsum[k + 2] = vsum[k] + v[k];
                        x.Enqueue(k + 2);
                    }
                    if (k + 3 < n && vsum[k] + v[k] > vsum[k + 3])
                    {
                        vsum[k + 3] = vsum[k] + v[k];
                        x.Enqueue(k + 3);
                    }
                }
                var a = vsum[n - 1] + v[n - 1];
                var b = vsum[n - 2] + v[n - 2];
                Console.WriteLine(a - b > 0 ? a : b);
            }
        }
    }
}