

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(); 
		int sum=0;
        long[] ar = new long[n];
        for (int i=0; i<n; i++) {
        	ar[i]=s.nextLong();
        	
        }
        long max=ar[0];
        for (int i=1; i<n; i++) {
        	max=Math.max(max, ar[i]);
        	if(max>ar[i]) {
        		sum+=max-ar[i];
        		ar[i]=max;
        		
        	}
        }
        System.out.println(sum);
        
      
	}
	
}
