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

namespace procon
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var n = int.Parse(Console.ReadLine());
            var inputs = Console.ReadLine().Split().Select(int.Parse).ToArray();

            var tmp = 0;
            var take_sum = 0;
            var not_sum = 0;
            
            for (int i = 0; i < n; i++)
            {
                tmp = not_sum + inputs[i];
                not_sum = take_sum > not_sum ? take_sum : not_sum;
                take_sum = tmp;
            }
            Console.WriteLine(take_sum > not_sum ? take_sum : not_sum);
        }
    }
}