using System;
using System.IO;

class Program
{
    static void Main(string[] args) {
        var scan = new Scanner();
        var writer = new StreamWriter(Console.OpenStandardOutput()) {AutoFlush = false};
        Console.SetOut(writer);
        Console.WriteLine(Solve(scan));
        Console.Out.Flush();
    }
    static int Solve(Scanner scan) {
        var N = scan.NextInt();
        var A = scan.ArrayInt(N);
        var len = A.Length;
        var temp = 0;
        var sum = 0;
        for (int i = 0; i < len; i++) {
            if (temp < A[i]) temp = A[i];
            else sum += temp - A[i];
        }
        return sum;
    }
}

class Scanner
{
    string[] s;
    int i;
    public Scanner() {
        s = new string[0];
        i = 0;
    }
    public string Next() {
        if (i < s.Length) return s[i++];
        string str = Console.ReadLine();
        while (str == "") str = Console.ReadLine();
        s = str.Split(' ', StringSplitOptions.RemoveEmptyEntries);
        if (s.Length == 0) return Next();
        i = 0;
        return s[i++];
    }
    public int NextInt() => int.Parse(Next());
    public int[] ArrayInt(int len, int add = 0) {
        var array = new int[len];
        for (int i = 0; i < len; i++) array[i] = NextInt() + add;
        return array;
    }
}