using System;
using System.Text;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using static System.Console;
using static System.Math;
namespace atcoder151
{
    public class MainClass
    {
        public static void Main(string[] args)
        {
            new MainClass().Solve(new ConsoleInput(Console.In, ' '));
        }

        public void Solve(ConsoleInput cin)
        {
            //string[] array = Console.ReadLine().Split(' ').ToArray();
            int n = int.Parse(Console.ReadLine());
            //Console.WriteLine(n);
            int[] num_array = cin.ReadIntArray(n);
            List<int> list = new List<int>();            

            int min = num_array[0];
            //WriteLine(min);
            for (int i =0; i< n; i++) {

                if (num_array[i] == min) {
                    list.Add(0);
                }
                else if (num_array[i] > min) {
                    //list.Add(0);
                    min = num_array[i];
                    list.Add(0);
                } else if (num_array[i] < min) {
                    list.Add(min - num_array[i]);
                }
                
            }

            WriteLine(list.Sum());
        }


        public class ConsoleInput
        {
            //string[] arr;
            //int x;
            //int y;
            //        for (int i = 0; i<n; i++)
            //        {
            //            arr = Console.ReadLine().Split(' ').ToArray();
            //x = int.Parse(arr[0]);
            //y = int.Parse(arr[1]);
            //var power = Math.Sqrt(Math.Pow(x, 2) + Math.Pow(y, 2));
            //            if (power <= d)
            //            {
            //                counter++;
            //            }
            //        }
            private readonly System.IO.TextReader _stream;
            private char _separator = ' ';
            private Queue<string> inputStream;
            public ConsoleInput(System.IO.TextReader stream, char separator = ' ')
            {
                this._separator = separator;
                this._stream = stream;
                inputStream = new Queue<string>();
            }
            public string Read
            {
                get
                {
                    if (inputStream.Count != 0) return inputStream.Dequeue();
                    string[] tmp = _stream.ReadLine().Split(_separator);
                    for (int i = 0; i < tmp.Length; ++i)
                        inputStream.Enqueue(tmp[i]);
                    return inputStream.Dequeue();
                }
            }
            public string ReadLine { get { return _stream.ReadLine(); } }
            public int ReadInt { get { return int.Parse(Read); } }
            public long ReadLong { get { return long.Parse(Read); } }
            public double ReadDouble { get { return double.Parse(Read); } }
            public string[] ReadStrArray(long N) { var ret = new string[N]; for (long i = 0; i < N; ++i) ret[i] = Read; return ret; }
            public int[] ReadIntArray(long N) { var ret = new int[N]; for (long i = 0; i < N; ++i) ret[i] = ReadInt; return ret; }
            public long[] ReadLongArray(long N) { var ret = new long[N]; for (long i = 0; i < N; ++i) ret[i] = ReadLong; return ret; }

        }
    }
}
