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