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

class Program
{
    static void Main(string[] args)
    {
        var sol = new Solve();
        sol.Exec();
    }
}

class Solve
{
    public void Exec()
    {
        var N = int.Parse(Console.ReadLine());
        var A = Console.ReadLine().Split().Select(int.Parse).ToArray();

        var acumFoward = new List<long>() { 0 };
        var acumBack = new List<long>() { 0 };
        for (var i = 1; i < 2 * N; i+=2)
        {
            acumFoward.Add(acumFoward[acumFoward.Count - 1] + A[i - 1] - A[i]);
            acumBack.Add(acumBack[acumBack.Count - 1] + A[A.Length - 1 - i + 1] - A[A.Length - 1 - i]);
        }

        var ans = 0L;
        for (var i = 0; i <= N; i++)
        {
            ans = Math.Max(ans, acumFoward[i] + acumBack[N - i]);
        }

        Console.WriteLine(ans);
    }
}

public class Util
{
}