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

namespace No45_2 {
    public class Program {
        public static void Main(string[] args){
            var n = int.Parse(Console.ReadLine());
            var sushiList = new List<int>{0};
            sushiList.AddRange(Console.ReadLine().Split().ToList().ConvertAll(int.Parse));

            var dp = new List<int> {sushiList[0], sushiList[1], sushiList[n == 1 ? 1 : 2]};
            for(var i = 3; i <= n; i++){
                dp.Add(Math.Max(dp[i - 3], dp[i - 2]) + sushiList[i]);
            }

            Console.WriteLine(Math.Max(dp[n], dp[n - 1]));
        }
    }
}