

import java.io.BufferedReader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Scanner;
import java.util.Set;
import java.util.StringTokenizer;


public class Main {
	 static class FastReader 
	    { 
	        BufferedReader br; 
	        StringTokenizer st; 
	       
	  
	        public FastReader() 
	        { 
	            br = new BufferedReader(new
	                     InputStreamReader(System.in)); 
	        } 
	  
	        String next() 
	        { 
	            while (st == null || !st.hasMoreTokens()) 
	            { 
	                try
	                { 
	                    st = new StringTokenizer(br.readLine()); 
	                } 
	                catch (IOException  e) 
	                { 
	                    e.printStackTrace(); 
	                } 
	            } 
	            return st.nextToken();
	            
	        } 
	  
	        int nextInt() 
	        { 
	            return Integer.parseInt(next()); 
	        } 
	  
	        long nextLong() 
	        { 
	            return Long.parseLong(next()); 
	        } 
	  
	        double nextDouble() 
	        { 
	            return Double.parseDouble(next()); 
	        } 
	  
	        String nextLine() 
	        { 
	            String str = ""; 
	            try
	            { 
	                str = br.readLine(); 
	            } 
	            catch (IOException e) 
	            { 
	                e.printStackTrace(); 
	            } 
	            return str; 
	        }

			public Character charAt(int i) {
				// TODO Auto-generated method stub
				return null;
			} 
	    } 
	public static boolean solve(long r, long g, long b, long w) {
		 if((r%2+g%2+b%2+w%2)>1)return false;
		 else return true;
	}
	public static void main(String[] args)throws IOException  {
		FastReader s=new FastReader();		
		int n = s.nextInt(); 
		long sum=0;
        long[] ar = new long[n];
        for (int i=0; i<n; i++) {
        	ar[i]=s.nextLong();
        	
        }
        for (int i=1; i<n; i++) {
        	if(ar[i-1]>ar[i]) {
        		sum+=ar[i-1]-ar[i];
        		ar[i]=ar[i-1];
        		
        	}
        }
        System.out.println(sum);
        
      
	}
	
} import java.io.BufferedReader; BufferedReader java.io import java.util.ArrayList; ArrayList java.util import java.util.Arrays; Arrays java.util import java.util.Collections; Collections java.util import java.util.HashMap; HashMap java.util import java.util.HashSet; HashSet java.util import java.util.List; List java.util import java.util.Map; Map java.util import java.io.IOException; IOException java.io import java.io.InputStreamReader; InputStreamReader java.io import java.util.Scanner; Scanner java.util import java.util.Set; Set java.util import java.util.StringTokenizer; StringTokenizer java.util public class Main {
	 static class FastReader 
	    { 
	        BufferedReader br; 
	        StringTokenizer st; 
	       
	  
	        public FastReader() 
	        { 
	            br = new BufferedReader(new
	                     InputStreamReader(System.in)); 
	        } 
	  
	        String next() 
	        { 
	            while (st == null || !st.hasMoreTokens()) 
	            { 
	                try
	                { 
	                    st = new StringTokenizer(br.readLine()); 
	                } 
	                catch (IOException  e) 
	                { 
	                    e.printStackTrace(); 
	                } 
	            } 
	            return st.nextToken();
	            
	        } 
	  
	        int nextInt() 
	        { 
	            return Integer.parseInt(next()); 
	        } 
	  
	        long nextLong() 
	        { 
	            return Long.parseLong(next()); 
	        } 
	  
	        double nextDouble() 
	        { 
	            return Double.parseDouble(next()); 
	        } 
	  
	        String nextLine() 
	        { 
	            String str = ""; 
	            try
	            { 
	                str = br.readLine(); 
	            } 
	            catch (IOException e) 
	            { 
	                e.printStackTrace(); 
	            } 
	            return str; 
	        }

			public Character charAt(int i) {
				// TODO Auto-generated method stub
				return null;
			} 
	    } 
	public static boolean solve(long r, long g, long b, long w) {
		 if((r%2+g%2+b%2+w%2)>1)return false;
		 else return true;
	}
	public static void main(String[] args)throws IOException  {
		FastReader s=new FastReader();		
		int n = s.nextInt(); 
		long sum=0;
        long[] ar = new long[n];
        for (int i=0; i<n; i++) {
        	ar[i]=s.nextLong();
        	
        }
        for (int i=1; i<n; i++) {
        	if(ar[i-1]>ar[i]) {
        		sum+=ar[i-1]-ar[i];
        		ar[i]=ar[i-1];
        		
        	}
        }
        System.out.println(sum);
        
      
	}
	
} Main public static boolean solve(long r, long g, long b, long w) {
		 if((r%2+g%2+b%2+w%2)>1)return false;
		 else return true;
	} solve {
		 if((r%2+g%2+b%2+w%2)>1)return false;
		 else return true;
	} if((r%2+g%2+b%2+w%2)>1)return false;
		 else return true; (r%2+g%2+b%2+w%2)>1 (r%2+g%2+b%2+w%2) b%2 r%2+g%2+b%2+w%2 r%2 r 2 g%2 g 2 b%2 b 2 w%2 w 2 1 return false; false return true; true long r r long g g long b b long w w public static void main(String[] args)throws IOException  {
		FastReader s=new FastReader();		
		int n = s.nextInt(); 
		long sum=0;
        long[] ar = new long[n];
        for (int i=0; i<n; i++) {
        	ar[i]=s.nextLong();
        	
        }
        for (int i=1; i<n; i++) {
        	if(ar[i-1]>ar[i]) {
        		sum+=ar[i-1]-ar[i];
        		ar[i]=ar[i-1];
        		
        	}
        }
        System.out.println(sum);
        
      
	} main {
		FastReader s=new FastReader();		
		int n = s.nextInt(); 
		long sum=0;
        long[] ar = new long[n];
        for (int i=0; i<n; i++) {
        	ar[i]=s.nextLong();
        	
        }
        for (int i=1; i<n; i++) {
        	if(ar[i-1]>ar[i]) {
        		sum+=ar[i-1]-ar[i];
        		ar[i]=ar[i-1];
        		
        	}
        }
        System.out.println(sum);
        
      
	} FastReader s=new FastReader(); s new FastReader() int n = s.nextInt(); n s.nextInt() s.nextInt s long sum=0; sum 0 long[] ar = new long[n]; ar new long[n] n for (int i=0; i<n; i++) {
        	ar[i]=s.nextLong();
        	
        } int i=0; int i=0; i 0 i<n i n i++ i++ i {
        	ar[i]=s.nextLong();
        	
        } {
        	ar[i]=s.nextLong();
        	
        } ar[i]=s.nextLong() ar[i] ar i s.nextLong() s.nextLong s for (int i=1; i<n; i++) {
        	if(ar[i-1]>ar[i]) {
        		sum+=ar[i-1]-ar[i];
        		ar[i]=ar[i-1];
        		
        	}
        } int i=1; int i=1; i 1 i<n i n i++ i++ i {
        	if(ar[i-1]>ar[i]) {
        		sum+=ar[i-1]-ar[i];
        		ar[i]=ar[i-1];
        		
        	}
        } {
        	if(ar[i-1]>ar[i]) {
        		sum+=ar[i-1]-ar[i];
        		ar[i]=ar[i-1];
        		
        	}
        } if(ar[i-1]>ar[i]) {
        		sum+=ar[i-1]-ar[i];
        		ar[i]=ar[i-1];
        		
        	} ar[i-1]>ar[i] ar[i-1] ar i-1 i 1 ar[i] ar i {
        		sum+=ar[i-1]-ar[i];
        		ar[i]=ar[i-1];
        		
        	} sum+=ar[i-1]-ar[i] sum ar[i-1]-ar[i] ar[i-1] ar i-1 i 1 ar[i] ar i ar[i]=ar[i-1] ar[i] ar i ar[i-1] ar i-1 i 1 System.out.println(sum) System.out.println System.out System System.out sum String[] args args static class FastReader 
	    { 
	        BufferedReader br; 
	        StringTokenizer st; 
	       
	  
	        public FastReader() 
	        { 
	            br = new BufferedReader(new
	                     InputStreamReader(System.in)); 
	        } 
	  
	        String next() 
	        { 
	            while (st == null || !st.hasMoreTokens()) 
	            { 
	                try
	                { 
	                    st = new StringTokenizer(br.readLine()); 
	                } 
	                catch (IOException  e) 
	                { 
	                    e.printStackTrace(); 
	                } 
	            } 
	            return st.nextToken();
	            
	        } 
	  
	        int nextInt() 
	        { 
	            return Integer.parseInt(next()); 
	        } 
	  
	        long nextLong() 
	        { 
	            return Long.parseLong(next()); 
	        } 
	  
	        double nextDouble() 
	        { 
	            return Double.parseDouble(next()); 
	        } 
	  
	        String nextLine() 
	        { 
	            String str = ""; 
	            try
	            { 
	                str = br.readLine(); 
	            } 
	            catch (IOException e) 
	            { 
	                e.printStackTrace(); 
	            } 
	            return str; 
	        }

			public Character charAt(int i) {
				// TODO Auto-generated method stub
				return null;
			} 
	    } FastReader BufferedReader br; br StringTokenizer st; st public FastReader() 
	        { 
	            br = new BufferedReader(new
	                     InputStreamReader(System.in)); 
	        } FastReader { 
	            br = new BufferedReader(new
	                     InputStreamReader(System.in)); 
	        } br = new BufferedReader(new
	                     InputStreamReader(System.in)) br new BufferedReader(new
	                     InputStreamReader(System.in)) String next() 
	        { 
	            while (st == null || !st.hasMoreTokens()) 
	            { 
	                try
	                { 
	                    st = new StringTokenizer(br.readLine()); 
	                } 
	                catch (IOException  e) 
	                { 
	                    e.printStackTrace(); 
	                } 
	            } 
	            return st.nextToken();
	            
	        } next { 
	            while (st == null || !st.hasMoreTokens()) 
	            { 
	                try
	                { 
	                    st = new StringTokenizer(br.readLine()); 
	                } 
	                catch (IOException  e) 
	                { 
	                    e.printStackTrace(); 
	                } 
	            } 
	            return st.nextToken();
	            
	        } while (st == null || !st.hasMoreTokens()) 
	            { 
	                try
	                { 
	                    st = new StringTokenizer(br.readLine()); 
	                } 
	                catch (IOException  e) 
	                { 
	                    e.printStackTrace(); 
	                } 
	            } st == null || !st.hasMoreTokens() st == null st null !st.hasMoreTokens() st.hasMoreTokens() st.hasMoreTokens st { 
	                try
	                { 
	                    st = new StringTokenizer(br.readLine()); 
	                } 
	                catch (IOException  e) 
	                { 
	                    e.printStackTrace(); 
	                } 
	            } try
	                { 
	                    st = new StringTokenizer(br.readLine()); 
	                } 
	                catch (IOException  e) 
	                { 
	                    e.printStackTrace(); 
	                } catch (IOException  e) 
	                { 
	                    e.printStackTrace(); 
	                } IOException  e { 
	                    e.printStackTrace(); 
	                } e.printStackTrace() e.printStackTrace e { 
	                    st = new StringTokenizer(br.readLine()); 
	                } st = new StringTokenizer(br.readLine()) st new StringTokenizer(br.readLine()) return st.nextToken(); st.nextToken() st.nextToken st int nextInt() 
	        { 
	            return Integer.parseInt(next()); 
	        } nextInt { 
	            return Integer.parseInt(next()); 
	        } return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next long nextLong() 
	        { 
	            return Long.parseLong(next()); 
	        } nextLong { 
	            return Long.parseLong(next()); 
	        } return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next double nextDouble() 
	        { 
	            return Double.parseDouble(next()); 
	        } nextDouble { 
	            return Double.parseDouble(next()); 
	        } return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double next() next String nextLine() 
	        { 
	            String str = ""; 
	            try
	            { 
	                str = br.readLine(); 
	            } 
	            catch (IOException e) 
	            { 
	                e.printStackTrace(); 
	            } 
	            return str; 
	        } nextLine { 
	            String str = ""; 
	            try
	            { 
	                str = br.readLine(); 
	            } 
	            catch (IOException e) 
	            { 
	                e.printStackTrace(); 
	            } 
	            return str; 
	        } String str = ""; str "" try
	            { 
	                str = br.readLine(); 
	            } 
	            catch (IOException e) 
	            { 
	                e.printStackTrace(); 
	            } catch (IOException e) 
	            { 
	                e.printStackTrace(); 
	            } IOException e { 
	                e.printStackTrace(); 
	            } e.printStackTrace() e.printStackTrace e { 
	                str = br.readLine(); 
	            } str = br.readLine() str br.readLine() br.readLine br return str; str public Character charAt(int i) {
				// TODO Auto-generated method stub
				return null;
			} charAt {
				// TODO Auto-generated method stub
				return null;
			} return null; null int i i public class Main {
	 static class FastReader 
	    { 
	        BufferedReader br; 
	        StringTokenizer st; 
	       
	  
	        public FastReader() 
	        { 
	            br = new BufferedReader(new
	                     InputStreamReader(System.in)); 
	        } 
	  
	        String next() 
	        { 
	            while (st == null || !st.hasMoreTokens()) 
	            { 
	                try
	                { 
	                    st = new StringTokenizer(br.readLine()); 
	                } 
	                catch (IOException  e) 
	                { 
	                    e.printStackTrace(); 
	                } 
	            } 
	            return st.nextToken();
	            
	        } 
	  
	        int nextInt() 
	        { 
	            return Integer.parseInt(next()); 
	        } 
	  
	        long nextLong() 
	        { 
	            return Long.parseLong(next()); 
	        } 
	  
	        double nextDouble() 
	        { 
	            return Double.parseDouble(next()); 
	        } 
	  
	        String nextLine() 
	        { 
	            String str = ""; 
	            try
	            { 
	                str = br.readLine(); 
	            } 
	            catch (IOException e) 
	            { 
	                e.printStackTrace(); 
	            } 
	            return str; 
	        }

			public Character charAt(int i) {
				// TODO Auto-generated method stub
				return null;
			} 
	    } 
	public static boolean solve(long r, long g, long b, long w) {
		 if((r%2+g%2+b%2+w%2)>1)return false;
		 else return true;
	}
	public static void main(String[] args)throws IOException  {
		FastReader s=new FastReader();		
		int n = s.nextInt(); 
		long sum=0;
        long[] ar = new long[n];
        for (int i=0; i<n; i++) {
        	ar[i]=s.nextLong();
        	
        }
        for (int i=1; i<n; i++) {
        	if(ar[i-1]>ar[i]) {
        		sum+=ar[i-1]-ar[i];
        		ar[i]=ar[i-1];
        		
        	}
        }
        System.out.println(sum);
        
      
	}
	
} public class Main {
	 static class FastReader 
	    { 
	        BufferedReader br; 
	        StringTokenizer st; 
	       
	  
	        public FastReader() 
	        { 
	            br = new BufferedReader(new
	                     InputStreamReader(System.in)); 
	        } 
	  
	        String next() 
	        { 
	            while (st == null || !st.hasMoreTokens()) 
	            { 
	                try
	                { 
	                    st = new StringTokenizer(br.readLine()); 
	                } 
	                catch (IOException  e) 
	                { 
	                    e.printStackTrace(); 
	                } 
	            } 
	            return st.nextToken();
	            
	        } 
	  
	        int nextInt() 
	        { 
	            return Integer.parseInt(next()); 
	        } 
	  
	        long nextLong() 
	        { 
	            return Long.parseLong(next()); 
	        } 
	  
	        double nextDouble() 
	        { 
	            return Double.parseDouble(next()); 
	        } 
	  
	        String nextLine() 
	        { 
	            String str = ""; 
	            try
	            { 
	                str = br.readLine(); 
	            } 
	            catch (IOException e) 
	            { 
	                e.printStackTrace(); 
	            } 
	            return str; 
	        }

			public Character charAt(int i) {
				// TODO Auto-generated method stub
				return null;
			} 
	    } 
	public static boolean solve(long r, long g, long b, long w) {
		 if((r%2+g%2+b%2+w%2)>1)return false;
		 else return true;
	}
	public static void main(String[] args)throws IOException  {
		FastReader s=new FastReader();		
		int n = s.nextInt(); 
		long sum=0;
        long[] ar = new long[n];
        for (int i=0; i<n; i++) {
        	ar[i]=s.nextLong();
        	
        }
        for (int i=1; i<n; i++) {
        	if(ar[i-1]>ar[i]) {
        		sum+=ar[i-1]-ar[i];
        		ar[i]=ar[i-1];
        		
        	}
        }
        System.out.println(sum);
        
      
	}
	
} Main


import java.io.BufferedReader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Scanner;
import java.util.Set;
import java.util.StringTokenizer;


public class Main {
	 static class FastReader 
	    { 
	        BufferedReader br; 
	        StringTokenizer st; 
	       
	  
	        public FastReader() 
	        { 
	            br = new BufferedReader(new
	                     InputStreamReader(System.in)); 
	        } 
	  
	        String next() 
	        { 
	            while (st == null || !st.hasMoreTokens()) 
	            { 
	                try
	                { 
	                    st = new StringTokenizer(br.readLine()); 
	                } 
	                catch (IOException  e) 
	                { 
	                    e.printStackTrace(); 
	                } 
	            } 
	            return st.nextToken();
	            
	        } 
	  
	        int nextInt() 
	        { 
	            return Integer.parseInt(next()); 
	        } 
	  
	        long nextLong() 
	        { 
	            return Long.parseLong(next()); 
	        } 
	  
	        double nextDouble() 
	        { 
	            return Double.parseDouble(next()); 
	        } 
	  
	        String nextLine() 
	        { 
	            String str = ""; 
	            try
	            { 
	                str = br.readLine(); 
	            } 
	            catch (IOException e) 
	            { 
	                e.printStackTrace(); 
	            } 
	            return str; 
	        }

			public Character charAt(int i) {
				// TODO Auto-generated method stub
				return null;
			} 
	    } 
	public static boolean solve(long r, long g, long b, long w) {
		 if((r%2+g%2+b%2+w%2)>1)return false;
		 else return true;
	}
	public static void main(String[] args)throws IOException  {
		FastReader s=new FastReader();		
		int n = s.nextInt(); 
		long sum=0;
        long[] ar = new long[n];
        for (int i=0; i<n; i++) {
        	ar[i]=s.nextLong();
        	
        }
        for (int i=1; i<n; i++) {
        	if(ar[i-1]>ar[i]) {
        		sum+=ar[i-1]-ar[i];
        		ar[i]=ar[i-1];
        		
        	}
        }
        System.out.println(sum);
        
      
	}
	
}
