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