import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner sc= new Scanner(System.in);
        int N = sc.nextInt();
        long[] A = new long [201000];
        for(int i =0; i < N; i++) A[i] = sc.nextLong();
        long humidai = 0;
        for(int i = 0; i < N - 1; i++){
          if(A[i] > A[i + 1]){
            humidai += (A[i] - A[i +1]);
            A[i+1] = A[i];
          }
        }
      System.out.println(humidai);
    } 
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner sc= new Scanner(System.in);
        int N = sc.nextInt();
        long[] A = new long [201000];
        for(int i =0; i < N; i++) A[i] = sc.nextLong();
        long humidai = 0;
        for(int i = 0; i < N - 1; i++){
          if(A[i] > A[i + 1]){
            humidai += (A[i] - A[i +1]);
            A[i+1] = A[i];
          }
        }
      System.out.println(humidai);
    } 
} Main public static void main(String[] args) {
        Scanner sc= new Scanner(System.in);
        int N = sc.nextInt();
        long[] A = new long [201000];
        for(int i =0; i < N; i++) A[i] = sc.nextLong();
        long humidai = 0;
        for(int i = 0; i < N - 1; i++){
          if(A[i] > A[i + 1]){
            humidai += (A[i] - A[i +1]);
            A[i+1] = A[i];
          }
        }
      System.out.println(humidai);
    } main {
        Scanner sc= new Scanner(System.in);
        int N = sc.nextInt();
        long[] A = new long [201000];
        for(int i =0; i < N; i++) A[i] = sc.nextLong();
        long humidai = 0;
        for(int i = 0; i < N - 1; i++){
          if(A[i] > A[i + 1]){
            humidai += (A[i] - A[i +1]);
            A[i+1] = A[i];
          }
        }
      System.out.println(humidai);
    } Scanner sc= new Scanner(System.in); sc new Scanner(System.in) int N = sc.nextInt(); N sc.nextInt() sc.nextInt sc long[] A = new long [201000]; A new long [201000] 201000 for(int i =0; i < N; i++) A[i] = sc.nextLong(); int i =0; int i =0; i 0 i < N i N i++ i++ i A[i] = sc.nextLong(); A[i] = sc.nextLong() A[i] A i sc.nextLong() sc.nextLong sc long humidai = 0; humidai 0 for(int i = 0; i < N - 1; i++){
          if(A[i] > A[i + 1]){
            humidai += (A[i] - A[i +1]);
            A[i+1] = A[i];
          }
        } int i = 0; int i = 0; i 0 i < N - 1 i N - 1 N 1 i++ i++ i {
          if(A[i] > A[i + 1]){
            humidai += (A[i] - A[i +1]);
            A[i+1] = A[i];
          }
        } {
          if(A[i] > A[i + 1]){
            humidai += (A[i] - A[i +1]);
            A[i+1] = A[i];
          }
        } if(A[i] > A[i + 1]){
            humidai += (A[i] - A[i +1]);
            A[i+1] = A[i];
          } A[i] > A[i + 1] A[i] A i A[i + 1] A i + 1 i 1 {
            humidai += (A[i] - A[i +1]);
            A[i+1] = A[i];
          } humidai += (A[i] - A[i +1]) humidai (A[i] - A[i +1]) A[i] A i A[i +1] A i +1 i 1 A[i+1] = A[i] A[i+1] A i+1 i 1 A[i] A i System.out.println(humidai) System.out.println System.out System System.out humidai String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc= new Scanner(System.in);
        int N = sc.nextInt();
        long[] A = new long [201000];
        for(int i =0; i < N; i++) A[i] = sc.nextLong();
        long humidai = 0;
        for(int i = 0; i < N - 1; i++){
          if(A[i] > A[i + 1]){
            humidai += (A[i] - A[i +1]);
            A[i+1] = A[i];
          }
        }
      System.out.println(humidai);
    } 
} public class Main {
    public static void main(String[] args) {
        Scanner sc= new Scanner(System.in);
        int N = sc.nextInt();
        long[] A = new long [201000];
        for(int i =0; i < N; i++) A[i] = sc.nextLong();
        long humidai = 0;
        for(int i = 0; i < N - 1; i++){
          if(A[i] > A[i + 1]){
            humidai += (A[i] - A[i +1]);
            A[i+1] = A[i];
          }
        }
      System.out.println(humidai);
    } 
} Main
import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner sc= new Scanner(System.in);
        int N = sc.nextInt();
        long[] A = new long [201000];
        for(int i =0; i < N; i++) A[i] = sc.nextLong();
        long humidai = 0;
        for(int i = 0; i < N - 1; i++){
          if(A[i] > A[i + 1]){
            humidai += (A[i] - A[i +1]);
            A[i+1] = A[i];
          }
        }
      System.out.println(humidai);
    } 
}