import java.io.*;
import 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.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) throws IOException {
		FastReader sc = new FastReader();
		int n = sc.nextInt();
		long count = 0;
		int max = Integer.MIN_VALUE;
		
		for (int i = 0; i < n; i++) {
		    int val = sc.nextInt();
		    max = Math.max(max, val);
		    
		    if (val < max) 
		        count += (max - val);
		}
		
		System.out.println(count);
	}
} import java.io.*; io.* java import java.util.*; util.* java 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) throws IOException {
		FastReader sc = new FastReader();
		int n = sc.nextInt();
		long count = 0;
		int max = Integer.MIN_VALUE;
		
		for (int i = 0; i < n; i++) {
		    int val = sc.nextInt();
		    max = Math.max(max, val);
		    
		    if (val < max) 
		        count += (max - val);
		}
		
		System.out.println(count);
	}
} Main public static void main (String[] args) throws IOException {
		FastReader sc = new FastReader();
		int n = sc.nextInt();
		long count = 0;
		int max = Integer.MIN_VALUE;
		
		for (int i = 0; i < n; i++) {
		    int val = sc.nextInt();
		    max = Math.max(max, val);
		    
		    if (val < max) 
		        count += (max - val);
		}
		
		System.out.println(count);
	} main {
		FastReader sc = new FastReader();
		int n = sc.nextInt();
		long count = 0;
		int max = Integer.MIN_VALUE;
		
		for (int i = 0; i < n; i++) {
		    int val = sc.nextInt();
		    max = Math.max(max, val);
		    
		    if (val < max) 
		        count += (max - val);
		}
		
		System.out.println(count);
	} FastReader sc = new FastReader(); sc new FastReader() int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc long count = 0; count 0 int max = Integer.MIN_VALUE; max Integer.MIN_VALUE Integer Integer.MIN_VALUE for (int i = 0; i < n; i++) {
		    int val = sc.nextInt();
		    max = Math.max(max, val);
		    
		    if (val < max) 
		        count += (max - val);
		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
		    int val = sc.nextInt();
		    max = Math.max(max, val);
		    
		    if (val < max) 
		        count += (max - val);
		} {
		    int val = sc.nextInt();
		    max = Math.max(max, val);
		    
		    if (val < max) 
		        count += (max - val);
		} int val = sc.nextInt(); val sc.nextInt() sc.nextInt sc max = Math.max(max, val) max Math.max(max, val) Math.max Math max val if (val < max) 
		        count += (max - val); val < max val max count += (max - val) count (max - val) max val System.out.println(count) System.out.println System.out System System.out count 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 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) throws IOException {
		FastReader sc = new FastReader();
		int n = sc.nextInt();
		long count = 0;
		int max = Integer.MIN_VALUE;
		
		for (int i = 0; i < n; i++) {
		    int val = sc.nextInt();
		    max = Math.max(max, val);
		    
		    if (val < max) 
		        count += (max - val);
		}
		
		System.out.println(count);
	}
} 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) throws IOException {
		FastReader sc = new FastReader();
		int n = sc.nextInt();
		long count = 0;
		int max = Integer.MIN_VALUE;
		
		for (int i = 0; i < n; i++) {
		    int val = sc.nextInt();
		    max = Math.max(max, val);
		    
		    if (val < max) 
		        count += (max - val);
		}
		
		System.out.println(count);
	}
} Main
import java.io.*;
import 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.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) throws IOException {
		FastReader sc = new FastReader();
		int n = sc.nextInt();
		long count = 0;
		int max = Integer.MIN_VALUE;
		
		for (int i = 0; i < n; i++) {
		    int val = sc.nextInt();
		    max = Math.max(max, val);
		    
		    if (val < max) 
		        count += (max - val);
		}
		
		System.out.println(count);
	}
}