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