import java.util.*;
class Main{

    public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int[] arr = new int[n];
    for(int i=0; i<n; i++) 
    arr[i] = sc.nextInt();
    long res =0;
    for(int i=1; i<n; i++) {
     if(arr[i-1]>arr[i]){
     res += arr[i-1]-arr[i];
     arr[i] = arr[i-1];
     }
     }
    System.out.println(res);
     //   System.out.println("Hello World");
    }
} import java.util.*; util.* java class Main{

    public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int[] arr = new int[n];
    for(int i=0; i<n; i++) 
    arr[i] = sc.nextInt();
    long res =0;
    for(int i=1; i<n; i++) {
     if(arr[i-1]>arr[i]){
     res += arr[i-1]-arr[i];
     arr[i] = arr[i-1];
     }
     }
    System.out.println(res);
     //   System.out.println("Hello World");
    }
} Main public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int[] arr = new int[n];
    for(int i=0; i<n; i++) 
    arr[i] = sc.nextInt();
    long res =0;
    for(int i=1; i<n; i++) {
     if(arr[i-1]>arr[i]){
     res += arr[i-1]-arr[i];
     arr[i] = arr[i-1];
     }
     }
    System.out.println(res);
     //   System.out.println("Hello World");
    } main {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int[] arr = new int[n];
    for(int i=0; i<n; i++) 
    arr[i] = sc.nextInt();
    long res =0;
    for(int i=1; i<n; i++) {
     if(arr[i-1]>arr[i]){
     res += arr[i-1]-arr[i];
     arr[i] = arr[i-1];
     }
     }
    System.out.println(res);
     //   System.out.println("Hello World");
    } 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 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] arr i sc.nextInt() sc.nextInt sc long res =0; res 0 for(int i=1; i<n; i++) {
     if(arr[i-1]>arr[i]){
     res += 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-1]>arr[i]){
     res += arr[i-1]-arr[i];
     arr[i] = arr[i-1];
     }
     } {
     if(arr[i-1]>arr[i]){
     res += arr[i-1]-arr[i];
     arr[i] = arr[i-1];
     }
     } if(arr[i-1]>arr[i]){
     res += arr[i-1]-arr[i];
     arr[i] = arr[i-1];
     } arr[i-1]>arr[i] arr[i-1] arr i-1 i 1 arr[i] arr i {
     res += arr[i-1]-arr[i];
     arr[i] = arr[i-1];
     } res += arr[i-1]-arr[i] res 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(res) System.out.println System.out System System.out res String args[] args
import java.util.*;
class Main{

    public static void main(String args[]){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int[] arr = new int[n];
    for(int i=0; i<n; i++) 
    arr[i] = sc.nextInt();
    long res =0;
    for(int i=1; i<n; i++) {
     if(arr[i-1]>arr[i]){
     res += arr[i-1]-arr[i];
     arr[i] = arr[i-1];
     }
     }
    System.out.println(res);
     //   System.out.println("Hello World");
    }
}
