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

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            int[] x = Console.ReadLine().Split().Select(int.Parse).ToArray();
            if (x.Length == 1) Console.WriteLine(x[0]);
            else if (x.Length == 2) Console.WriteLine(Math.Max(x[0],x[1]));
            else if (x.Length == 3) Console.WriteLine(Math.Max(x[0] + x[2],x[1]));
            else
            {
                int[] dp = new int[x.Length];
                dp[0] = x[0]; dp[1] = x[1]; dp[2] = x[0] + x[2];
                for (int i = 3; i < x.Length; i++)
                {
                    dp[i] = Math.Max(dp[i - 3],dp[i - 2]) + x[i];
                }
                Console.WriteLine(dp[x.Length - 1]);
            }
        }
    }
}