import java.util.*;
import java.io.*;
import java.lang.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();

        int[] arr = new int[n];

        long ans = 0;

        for (int i = 0; i<n; i++){
            arr[i] = sc.nextInt();
        }

        for (int i = 1; i<n; i++){
            if (arr[i] < arr[i-1]){
                ans += (arr[i-1]-arr[i]);
                arr[i] = arr[i-1];
            }
        }
        System.out.println(ans);
    }
} import java.util.*; util.* java import java.io.*; io.* java import java.lang.*; lang.* java public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();

        int[] arr = new int[n];

        long ans = 0;

        for (int i = 0; i<n; i++){
            arr[i] = sc.nextInt();
        }

        for (int i = 1; i<n; i++){
            if (arr[i] < arr[i-1]){
                ans += (arr[i-1]-arr[i]);
                arr[i] = arr[i-1];
            }
        }
        System.out.println(ans);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();

        int[] arr = new int[n];

        long ans = 0;

        for (int i = 0; i<n; i++){
            arr[i] = sc.nextInt();
        }

        for (int i = 1; i<n; i++){
            if (arr[i] < arr[i-1]){
                ans += (arr[i-1]-arr[i]);
                arr[i] = arr[i-1];
            }
        }
        System.out.println(ans);
    } main {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();

        int[] arr = new int[n];

        long ans = 0;

        for (int i = 0; i<n; i++){
            arr[i] = sc.nextInt();
        }

        for (int i = 1; i<n; i++){
            if (arr[i] < arr[i-1]){
                ans += (arr[i-1]-arr[i]);
                arr[i] = arr[i-1];
            }
        }
        System.out.println(ans);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int[] arr = new int[n]; arr new int[n] n long ans = 0; ans 0 for (int i = 0; i<n; i++){
            arr[i] = sc.nextInt();
        } int i = 0; int i = 0; i 0 i<n i n i++ i++ i {
            arr[i] = sc.nextInt();
        } {
            arr[i] = sc.nextInt();
        } arr[i] = sc.nextInt() arr[i] arr i sc.nextInt() sc.nextInt sc for (int i = 1; i<n; i++){
            if (arr[i] < arr[i-1]){
                ans += (arr[i-1]-arr[i]);
                arr[i] = arr[i-1];
            }
        } int i = 1; int i = 1; i 1 i<n i n i++ i++ i {
            if (arr[i] < arr[i-1]){
                ans += (arr[i-1]-arr[i]);
                arr[i] = arr[i-1];
            }
        } {
            if (arr[i] < arr[i-1]){
                ans += (arr[i-1]-arr[i]);
                arr[i] = arr[i-1];
            }
        } if (arr[i] < arr[i-1]){
                ans += (arr[i-1]-arr[i]);
                arr[i] = arr[i-1];
            } arr[i] < arr[i-1] arr[i] arr i arr[i-1] arr i-1 i 1 {
                ans += (arr[i-1]-arr[i]);
                arr[i] = arr[i-1];
            } ans += (arr[i-1]-arr[i]) ans (arr[i-1]-arr[i]) arr[i-1] arr i-1 i 1 arr[i] arr i arr[i] = arr[i-1] arr[i] arr i arr[i-1] arr i-1 i 1 System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();

        int[] arr = new int[n];

        long ans = 0;

        for (int i = 0; i<n; i++){
            arr[i] = sc.nextInt();
        }

        for (int i = 1; i<n; i++){
            if (arr[i] < arr[i-1]){
                ans += (arr[i-1]-arr[i]);
                arr[i] = arr[i-1];
            }
        }
        System.out.println(ans);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();

        int[] arr = new int[n];

        long ans = 0;

        for (int i = 0; i<n; i++){
            arr[i] = sc.nextInt();
        }

        for (int i = 1; i<n; i++){
            if (arr[i] < arr[i-1]){
                ans += (arr[i-1]-arr[i]);
                arr[i] = arr[i-1];
            }
        }
        System.out.println(ans);
    }
} Main
import java.util.*;
import java.io.*;
import java.lang.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();

        int[] arr = new int[n];

        long ans = 0;

        for (int i = 0; i<n; i++){
            arr[i] = sc.nextInt();
        }

        for (int i = 1; i<n; i++){
            if (arr[i] < arr[i-1]){
                ans += (arr[i-1]-arr[i]);
                arr[i] = arr[i-1];
            }
        }
        System.out.println(ans);
    }
}