using System;
using System.Linq;

namespace _45
{
    class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            int[] x = Console.ReadLine().Split().Select(int.Parse).ToArray();
            if (n == 1) Console.WriteLine(x[0]);
            else if (n == 2) Console.WriteLine(x.Max());
            else if (n == 3) Console.WriteLine(Math.Max(x[0] + x[2],x[1]));
            else
            {
                int[] dp = new int[n];
                dp[0] = x[0]; dp[1] = x[1]; dp[2] = dp[0] + x[2];
                for (int i = 3; i < n; i++)
                {
                    dp[i] = Math.Max(dp[i - 2],dp[i - 3]) + x[i];
                }
                Console.WriteLine(dp[n - 1]);
            }
        }
    }
}