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

        var left = 0;
        var right = 0;

        var ans = 0L;
        var correction = 0;
        for (var i = 0; i < N; i++)
        {
            if (acumFoward[left] > acumBack[right])
            {
                ans += acumFoward[left];
                left++;
                if (correction != 0)
                {
                    right -= correction;
                    correction = 0;
                }
            }
            else if (acumFoward[left] < acumBack[right])
            {
                ans += acumBack[right];
                right++;
                if (correction != 0)
                {
                    left -= correction;
                    correction = 0;
                }
            }
            else
            {
                if (i == N - 1)
                    left -= correction;

                ans += acumFoward[left];
                correction++;
                left++;
                right++;
            }
        }

        Console.WriteLine(ans);
    }
}

public class Util
{
}