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

namespace yukicoder
{
    public class Program
    {
        public static void Main()
        {
            var n = int.Parse(Console.ReadLine());
            var a = Console.ReadLine().Split().Select(x => long.Parse(x)).ToList();
            long s = 0;
            long v = 0;
            while (a.Count > 0)
            {
                while (a.Count > 0 && a[a.Count - 1] - a[a.Count - 2] >= v)
                {
                    s += a[a.Count - 1] - a[a.Count - 2];
                    a.RemoveAt(a.Count - 1);
                    a.RemoveAt(a.Count - 1);
                }
                if(a.Count > 0)
                {
                    v = a[a.Count - 1] - a[a.Count - 2];
                }
                while (a.Count > 0 && a[0] - a[1] >= v)
                {
                    s += a[0] - a[1];
                    a.RemoveAt(0);
                    a.RemoveAt(0);
                }
                if (a.Count > 0)
                {
                    v = a[0] - a[1];
                }
            }
            Console.WriteLine(s);
        }
    }
}