import java.io.*;
import java.util.*;
public class Main {
    static long startTime;
    static long endTime;
    static Boolean [] prime ;
    static int M=(int)1e9+7;
    static int MAX=Integer.MAX_VALUE;
    static int MIN=Integer.MIN_VALUE;
    static int SIZE = (int)1e9*2;
    static class FastReader{
        BufferedReader br;
        StringTokenizer st;

        public FastReader()
        {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
        }

        String next()
        {
            while (st == null || !st.hasMoreElements())
            {
                try
                {
                    st = new StringTokenizer(br.readLine());
                }
                catch (IOException  e)
                {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt()
        {
            return Integer.parseInt(next());
        }

        long nextLong()
        {
            return Long.parseLong(next());
        }

        double nextDouble()
        {
            return Double.parseDouble(next());
        }

        String nextLine()
        {
            String str = "";
            try
            {
                str = br.readLine();
            }
            catch (IOException e)
            {
                e.printStackTrace();
            }
            return str;
        }
    }
    static void printArray(int arr[])
    {
        int n = arr.length;
        for (int i = 0; i < n; ++i)
            System.out.print(arr[i] + " ");
        System.out.println();
    }
    static void printArray(long arr[])
    {
        int n = arr.length;
        for (int i = 0; i < n; ++i)
            System.out.print(arr[i] + " ");
        System.out.println();
    }
    static void printArray(Integer arr[])
    {
        int n = arr.length;
        for (int i = 0; i < n; ++i)
            System.out.print(arr[i] + " ");
        System.out.println();
    }
    static void printArray(Long arr[])
    {
        int n = arr.length;
        for (int i = 0; i < n; ++i)
            System.out.print(arr[i] + " ");
        System.out.println();
    }
    static void yes(){
        System.out.println("YES");
    }
    static void no(){
        System.out.println("NO");
    }
    public static int lowerBound
            (Integer[] array, int length, int value) {
        // Returns the index of the value or
        // if there is no value, returns the closest to the left.
        int low=-1; // arr[low]<=tar
        int hi=length;//arr[hi]>tar
        while (low+1<hi){ // while pointers are not neighboring(low+1!=hi)
            int mid=(low+hi)/2;
            if(array[mid]<=value){
                low=mid;
            }
            else {
                hi=mid;
            }
        }
        return low;// if no such element, returns -1.
    }
    public static int upperBound(Integer[] array, int length, int value){
        // returns the index of the value or
        // if the value does not exist, returns the closest to the right
        int low=-1; // arr[low]<tar
        int hi=length;// arr[hi]>=tar
        while (low+1<hi){// Eventually, pointers should be adjacent.
            int mid=(low+hi)>>1;
            if(array[mid]>=value){
                hi=mid;
            }
            else low=mid;
        }
        return hi;
    }
    public  static  int binarySearch(Integer [] arr, int length, int value){
       // returns the index of the targeted value or -1 if there is no value.
        int low=0;
        int hi=length-1;
        int ans=-1;
        while (low<=hi){
            int mid=(low+hi)>>1;
            if(arr[mid]>value){
                hi=mid-1;
            }
            else if(arr[mid]<value){
                low=mid+1;
            }
            else {
                ans=mid;
                break;
            }
        }
        return ans;
    }
    public static long gcd(long a, long b){
        if (b == 0)
            return a;
        else return gcd(b, a % b);
    }
    public  static  long countDivs(long n ){
        int cn=0;
        long sqr = (long)Math.sqrt(n);
        for (long i = 1; i<=sqr ; ++i) {
            if(n%i==0){
                ++cn;
            }
        }
        cn*=2;
        if(sqr*sqr==n) cn--;
        return cn;

    }
    static void prime(int  x) {
        //sieve algorithm. nlog(log(n)).
        prime=new Boolean[ (x+1)];
        Arrays.fill(prime,true);
        prime[0] = prime[1] = false;
        for (int  i = 2; i * i <= x ; i++)
            if (prime[i])
                for (int  j = i * i; j <= x; j += i)
                    prime[j] = false;
    }
    static int[] sum;
    static void cumulitiveSum( int [] arr){
        sum = new int[arr.length];
        sum[0]=arr[0];
        for (int i = 1; i <arr.length; i++) {
            sum[i]=arr[i]+sum[i-1];
        }
    }
    static boolean isEven(long x ){
        return x % 2 == 0;
    }
    static boolean isPrime(long x ){
        boolean flag = true;
        int sqr = (int)Math.sqrt(x);
        if(x<2) return false;
        for (int i = 2; i <=sqr; i++) {
            if(x%i==0){
                flag=false;
                break;
            }
        }
        return flag;
    }
    static long factorial( long x) {
        long total = 1;
        for (int i = 2; i <= x; i++)
            total *= i;
        return total;
    }
    static long power(long x, long n) {
        if (n == 0) {
            return 1;
        }

        long pow = power(x, n / 2L);
        if ((n & 1) == 1) {
            return x * pow * pow;
        }

        return pow * pow;
    }

    public static void main(String [] args) {
        startTime = System.currentTimeMillis();
       // int T = sc.nextInt();while (T--!=0)
        {
            solve();
        }
        endTime = System.currentTimeMillis();
        long duration= endTime-startTime;
        //System.out.println(duration);
    }

    // static Scanner sc = new Scanner(System.in);
    static FastReader sc = new FastReader();
    public static void solve()  {
//////////////////////////////////////////////////////////////////////
     int n =sc.nextInt();
     int [] arr = new int[n];
     int max=arr[0];
        for (int i = 0; i < n; i++) {
                arr[i]=sc.nextInt();
        }
        long sum=0;
        for (int i = 0; i < n; i++) {
                if(arr[i]<max){
                    sum+=arr[i]-max;
                }
                else max=arr[i];
        }
        System.out.println(-sum);
///////////////////////////////////////////////////////////////////////
    }

}


Measured memory_bytes: 54748