using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace No._45
{
    class Program
    {
        static void Main(string[] args)
        {
            Program program = new Program();

            program.code();
        }

        public void code()
        {
            int time = int.Parse(Console.ReadLine());

            String[] array= Console.ReadLine().Split(' ');

            Console.WriteLine(search(array, true, 0, time));
        }

        private int search(String[] array,Boolean flg, int depth, int times)
        {
            if(depth == times - 1)
            {
                if(flg)
                {
                    return int.Parse(array[depth]);
                } else
                {
                    return 0;
                }
            } else
            {
                int ans = search(array, true, depth + 1, times);

                if (flg)
                {
                    int temp = int.Parse(array[depth]) + search(array, false, depth + 1, times);

                    if (temp > ans)
                    {
                        ans = temp;
                    }

                }

                return ans;
            }
        }
    }
}