/* package whatever; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is 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.hasMoreElements()) 
            { 
                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 static void main(String[] args) 
    { 
        FastReader sc=new FastReader(); 
		int n=sc.nextInt();
		int[] a=new int[n];
		
		for(int i=0;i<n;i++) a[i]=sc.nextInt();
		long sum=0;
		for(int i=1;i<n;i++){
			if(a[i]<a[i-1]){
				sum+=a[i-1]-a[i];
				a[i]=a[i-1];
			}
		}
		System.out.println(sum);
	
    	
    }
} import java.util.*; util.* java import java.lang.*; lang.* java import java.io.*; io.* java class Main
{
	
    static class FastReader 
    { 
        BufferedReader br; 
        StringTokenizer st; 
  
        public FastReader() 
        { 
            br = new BufferedReader(new
                     InputStreamReader(System.in)); 
        } 
  
        String next() 
        { 
            while (st == null || !st.hasMoreElements()) 
            { 
                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 static void main(String[] args) 
    { 
        FastReader sc=new FastReader(); 
		int n=sc.nextInt();
		int[] a=new int[n];
		
		for(int i=0;i<n;i++) a[i]=sc.nextInt();
		long sum=0;
		for(int i=1;i<n;i++){
			if(a[i]<a[i-1]){
				sum+=a[i-1]-a[i];
				a[i]=a[i-1];
			}
		}
		System.out.println(sum);
	
    	
    }
} Main public static void main(String[] args) 
    { 
        FastReader sc=new FastReader(); 
		int n=sc.nextInt();
		int[] a=new int[n];
		
		for(int i=0;i<n;i++) a[i]=sc.nextInt();
		long sum=0;
		for(int i=1;i<n;i++){
			if(a[i]<a[i-1]){
				sum+=a[i-1]-a[i];
				a[i]=a[i-1];
			}
		}
		System.out.println(sum);
	
    	
    } main { 
        FastReader sc=new FastReader(); 
		int n=sc.nextInt();
		int[] a=new int[n];
		
		for(int i=0;i<n;i++) a[i]=sc.nextInt();
		long sum=0;
		for(int i=1;i<n;i++){
			if(a[i]<a[i-1]){
				sum+=a[i-1]-a[i];
				a[i]=a[i-1];
			}
		}
		System.out.println(sum);
	
    	
    } FastReader sc=new FastReader(); sc new FastReader() int n=sc.nextInt(); n sc.nextInt() sc.nextInt sc int[] a=new int[n]; a new int[n] n for(int i=0;i<n;i++) a[i]=sc.nextInt(); int i=0; int i=0; i 0 i<n i n i++ i++ i a[i]=sc.nextInt(); a[i]=sc.nextInt() a[i] a i sc.nextInt() sc.nextInt sc long sum=0; sum 0 for(int i=1;i<n;i++){
			if(a[i]<a[i-1]){
				sum+=a[i-1]-a[i];
				a[i]=a[i-1];
			}
		} int i=1; int i=1; i 1 i<n i n i++ i++ i {
			if(a[i]<a[i-1]){
				sum+=a[i-1]-a[i];
				a[i]=a[i-1];
			}
		} {
			if(a[i]<a[i-1]){
				sum+=a[i-1]-a[i];
				a[i]=a[i-1];
			}
		} if(a[i]<a[i-1]){
				sum+=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 {
				sum+=a[i-1]-a[i];
				a[i]=a[i-1];
			} sum+=a[i-1]-a[i] sum a[i-1]-a[i] 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(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.hasMoreElements()) 
            { 
                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; 
        } 
    } 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.hasMoreElements()) 
            { 
                try
                { 
                    st = new StringTokenizer(br.readLine()); 
                } 
                catch (IOException  e) 
                { 
                    e.printStackTrace(); 
                } 
            } 
            return st.nextToken(); 
        } next { 
            while (st == null || !st.hasMoreElements()) 
            { 
                try
                { 
                    st = new StringTokenizer(br.readLine()); 
                } 
                catch (IOException  e) 
                { 
                    e.printStackTrace(); 
                } 
            } 
            return st.nextToken(); 
        } while (st == null || !st.hasMoreElements()) 
            { 
                try
                { 
                    st = new StringTokenizer(br.readLine()); 
                } 
                catch (IOException  e) 
                { 
                    e.printStackTrace(); 
                } 
            } st == null || !st.hasMoreElements() st == null st null !st.hasMoreElements() st.hasMoreElements() st.hasMoreElements 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
/* package whatever; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is 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.hasMoreElements()) 
            { 
                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 static void main(String[] args) 
    { 
        FastReader sc=new FastReader(); 
		int n=sc.nextInt();
		int[] a=new int[n];
		
		for(int i=0;i<n;i++) a[i]=sc.nextInt();
		long sum=0;
		for(int i=1;i<n;i++){
			if(a[i]<a[i-1]){
				sum+=a[i-1]-a[i];
				a[i]=a[i-1];
			}
		}
		System.out.println(sum);
	
    	
    }
}