
import 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[n];
		for(int i=0;i<n;i++) {
			a[i]=sc.nextLong();
		}
		long ans=0;
		long max=a[0];
		for(int i=0;i<n;i++) {
			if(a[i]>=max) {
				max=a[i];
				continue;
			}
			else {
				ans+=max-a[i];
			
				
				
			}
		}
		System.out.println(ans);
					
				
			}
		
	}
	   
 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 a[]=new long[n];
		for(int i=0;i<n;i++) {
			a[i]=sc.nextLong();
		}
		long ans=0;
		long max=a[0];
		for(int i=0;i<n;i++) {
			if(a[i]>=max) {
				max=a[i];
				continue;
			}
			else {
				ans+=max-a[i];
			
				
				
			}
		}
		System.out.println(ans);
					
				
			}
		
	} Main public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
			int n=sc.nextInt();
		long a[]=new long[n];
		for(int i=0;i<n;i++) {
			a[i]=sc.nextLong();
		}
		long ans=0;
		long max=a[0];
		for(int i=0;i<n;i++) {
			if(a[i]>=max) {
				max=a[i];
				continue;
			}
			else {
				ans+=max-a[i];
			
				
				
			}
		}
		System.out.println(ans);
					
				
			} main {
		Scanner sc=new Scanner(System.in);
			int n=sc.nextInt();
		long a[]=new long[n];
		for(int i=0;i<n;i++) {
			a[i]=sc.nextLong();
		}
		long ans=0;
		long max=a[0];
		for(int i=0;i<n;i++) {
			if(a[i]>=max) {
				max=a[i];
				continue;
			}
			else {
				ans+=max-a[i];
			
				
				
			}
		}
		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 long a[]=new long[n]; a new long[n] n 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]=sc.nextLong() a[i] a i sc.nextLong() sc.nextLong sc long ans=0; ans 0 long max=a[0]; max a[0] a 0 for(int i=0;i<n;i++) {
			if(a[i]>=max) {
				max=a[i];
				continue;
			}
			else {
				ans+=max-a[i];
			
				
				
			}
		} int i=0; int i=0; i 0 i<n i n i++ i++ i {
			if(a[i]>=max) {
				max=a[i];
				continue;
			}
			else {
				ans+=max-a[i];
			
				
				
			}
		} {
			if(a[i]>=max) {
				max=a[i];
				continue;
			}
			else {
				ans+=max-a[i];
			
				
				
			}
		} if(a[i]>=max) {
				max=a[i];
				continue;
			}
			else {
				ans+=max-a[i];
			
				
				
			} a[i]>=max a[i] a i max {
				max=a[i];
				continue;
			} max=a[i] max a[i] a i continue; {
				ans+=max-a[i];
			
				
				
			} ans+=max-a[i] ans max-a[i] max a[i] a i System.out.println(ans) System.out.println System.out System System.out ans 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[n];
		for(int i=0;i<n;i++) {
			a[i]=sc.nextLong();
		}
		long ans=0;
		long max=a[0];
		for(int i=0;i<n;i++) {
			if(a[i]>=max) {
				max=a[i];
				continue;
			}
			else {
				ans+=max-a[i];
			
				
				
			}
		}
		System.out.println(ans);
					
				
			}
		
	} public class Main {

	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
			int n=sc.nextInt();
		long a[]=new long[n];
		for(int i=0;i<n;i++) {
			a[i]=sc.nextLong();
		}
		long ans=0;
		long max=a[0];
		for(int i=0;i<n;i++) {
			if(a[i]>=max) {
				max=a[i];
				continue;
			}
			else {
				ans+=max-a[i];
			
				
				
			}
		}
		System.out.println(ans);
					
				
			}
		
	} Main

import 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[n];
		for(int i=0;i<n;i++) {
			a[i]=sc.nextLong();
		}
		long ans=0;
		long max=a[0];
		for(int i=0;i<n;i++) {
			if(a[i]>=max) {
				max=a[i];
				continue;
			}
			else {
				ans+=max-a[i];
			
				
				
			}
		}
		System.out.println(ans);
					
				
			}
		
	}
	   

