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

public class Main {


    public static void main(String[] args) throws Exception {

        FastReader fs = new FastReader();
        out = new PrintWriter(new BufferedOutputStream(System.out));

       int n = fs.nextInt();
       int[] inp = new int[n];

       for(int i=0 ; i<n ; i++){
           inp[i] = fs.nextInt();
       }

       long ans = 0 ;

       for(int i=0 ; i<n ; i++){
           int max = inp[i];
           for(int j=i+1 ; j<n ; j++){
               if(inp[j]<max){
                   ans += (max-inp[j]);
               }else{
                   i = j - 1 ;
                   break;
               }
               if(j==n-1){
                   i = j;
               }
           }
       }

       out.println(ans);

        out.close();

    }

    //-----------PrintWriter for faster output---------------------------------
    public static PrintWriter out;

    //-----------MyScanner class for faster input----------
    public 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;
        }

    }
    //--------------------------------------------------------
}
 import java.io.*; io.* java import java.util.*; util.* java public class Main {


    public static void main(String[] args) throws Exception {

        FastReader fs = new FastReader();
        out = new PrintWriter(new BufferedOutputStream(System.out));

       int n = fs.nextInt();
       int[] inp = new int[n];

       for(int i=0 ; i<n ; i++){
           inp[i] = fs.nextInt();
       }

       long ans = 0 ;

       for(int i=0 ; i<n ; i++){
           int max = inp[i];
           for(int j=i+1 ; j<n ; j++){
               if(inp[j]<max){
                   ans += (max-inp[j]);
               }else{
                   i = j - 1 ;
                   break;
               }
               if(j==n-1){
                   i = j;
               }
           }
       }

       out.println(ans);

        out.close();

    }

    //-----------PrintWriter for faster output---------------------------------
    public static PrintWriter out;

    //-----------MyScanner class for faster input----------
    public 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;
        }

    }
    //--------------------------------------------------------
} Main //-----------PrintWriter for faster output---------------------------------
    public static PrintWriter out; out public static void main(String[] args) throws Exception {

        FastReader fs = new FastReader();
        out = new PrintWriter(new BufferedOutputStream(System.out));

       int n = fs.nextInt();
       int[] inp = new int[n];

       for(int i=0 ; i<n ; i++){
           inp[i] = fs.nextInt();
       }

       long ans = 0 ;

       for(int i=0 ; i<n ; i++){
           int max = inp[i];
           for(int j=i+1 ; j<n ; j++){
               if(inp[j]<max){
                   ans += (max-inp[j]);
               }else{
                   i = j - 1 ;
                   break;
               }
               if(j==n-1){
                   i = j;
               }
           }
       }

       out.println(ans);

        out.close();

    } main {

        FastReader fs = new FastReader();
        out = new PrintWriter(new BufferedOutputStream(System.out));

       int n = fs.nextInt();
       int[] inp = new int[n];

       for(int i=0 ; i<n ; i++){
           inp[i] = fs.nextInt();
       }

       long ans = 0 ;

       for(int i=0 ; i<n ; i++){
           int max = inp[i];
           for(int j=i+1 ; j<n ; j++){
               if(inp[j]<max){
                   ans += (max-inp[j]);
               }else{
                   i = j - 1 ;
                   break;
               }
               if(j==n-1){
                   i = j;
               }
           }
       }

       out.println(ans);

        out.close();

    } FastReader fs = new FastReader(); fs new FastReader() out = new PrintWriter(new BufferedOutputStream(System.out)) out new PrintWriter(new BufferedOutputStream(System.out)) int n = fs.nextInt(); n fs.nextInt() fs.nextInt fs int[] inp = new int[n]; inp new int[n] n for(int i=0 ; i<n ; i++){
           inp[i] = fs.nextInt();
       } int i=0 ; int i=0 ; i 0 i<n i n i++ i++ i {
           inp[i] = fs.nextInt();
       } {
           inp[i] = fs.nextInt();
       } inp[i] = fs.nextInt() inp[i] inp i fs.nextInt() fs.nextInt fs long ans = 0 ; ans 0 for(int i=0 ; i<n ; i++){
           int max = inp[i];
           for(int j=i+1 ; j<n ; j++){
               if(inp[j]<max){
                   ans += (max-inp[j]);
               }else{
                   i = j - 1 ;
                   break;
               }
               if(j==n-1){
                   i = j;
               }
           }
       } int i=0 ; int i=0 ; i 0 i<n i n i++ i++ i {
           int max = inp[i];
           for(int j=i+1 ; j<n ; j++){
               if(inp[j]<max){
                   ans += (max-inp[j]);
               }else{
                   i = j - 1 ;
                   break;
               }
               if(j==n-1){
                   i = j;
               }
           }
       } {
           int max = inp[i];
           for(int j=i+1 ; j<n ; j++){
               if(inp[j]<max){
                   ans += (max-inp[j]);
               }else{
                   i = j - 1 ;
                   break;
               }
               if(j==n-1){
                   i = j;
               }
           }
       } int max = inp[i]; max inp[i] inp i for(int j=i+1 ; j<n ; j++){
               if(inp[j]<max){
                   ans += (max-inp[j]);
               }else{
                   i = j - 1 ;
                   break;
               }
               if(j==n-1){
                   i = j;
               }
           } int j=i+1 ; int j=i+1 ; j i+1 i 1 j<n j n j++ j++ j {
               if(inp[j]<max){
                   ans += (max-inp[j]);
               }else{
                   i = j - 1 ;
                   break;
               }
               if(j==n-1){
                   i = j;
               }
           } {
               if(inp[j]<max){
                   ans += (max-inp[j]);
               }else{
                   i = j - 1 ;
                   break;
               }
               if(j==n-1){
                   i = j;
               }
           } if(inp[j]<max){
                   ans += (max-inp[j]);
               }else{
                   i = j - 1 ;
                   break;
               } inp[j]<max inp[j] inp j max {
                   ans += (max-inp[j]);
               } ans += (max-inp[j]) ans (max-inp[j]) max inp[j] inp j {
                   i = j - 1 ;
                   break;
               } i = j - 1 i j - 1 j 1 break; if(j==n-1){
                   i = j;
               } j==n-1 j n-1 n 1 {
                   i = j;
               } i = j i j out.println(ans) out.println out ans out.close() out.close out String[] args args public 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 {


    public static void main(String[] args) throws Exception {

        FastReader fs = new FastReader();
        out = new PrintWriter(new BufferedOutputStream(System.out));

       int n = fs.nextInt();
       int[] inp = new int[n];

       for(int i=0 ; i<n ; i++){
           inp[i] = fs.nextInt();
       }

       long ans = 0 ;

       for(int i=0 ; i<n ; i++){
           int max = inp[i];
           for(int j=i+1 ; j<n ; j++){
               if(inp[j]<max){
                   ans += (max-inp[j]);
               }else{
                   i = j - 1 ;
                   break;
               }
               if(j==n-1){
                   i = j;
               }
           }
       }

       out.println(ans);

        out.close();

    }

    //-----------PrintWriter for faster output---------------------------------
    public static PrintWriter out;

    //-----------MyScanner class for faster input----------
    public 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 class Main {


    public static void main(String[] args) throws Exception {

        FastReader fs = new FastReader();
        out = new PrintWriter(new BufferedOutputStream(System.out));

       int n = fs.nextInt();
       int[] inp = new int[n];

       for(int i=0 ; i<n ; i++){
           inp[i] = fs.nextInt();
       }

       long ans = 0 ;

       for(int i=0 ; i<n ; i++){
           int max = inp[i];
           for(int j=i+1 ; j<n ; j++){
               if(inp[j]<max){
                   ans += (max-inp[j]);
               }else{
                   i = j - 1 ;
                   break;
               }
               if(j==n-1){
                   i = j;
               }
           }
       }

       out.println(ans);

        out.close();

    }

    //-----------PrintWriter for faster output---------------------------------
    public static PrintWriter out;

    //-----------MyScanner class for faster input----------
    public 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;
        }

    }
    //--------------------------------------------------------
} Main
import java.io.*;
import java.util.*;

public class Main {


    public static void main(String[] args) throws Exception {

        FastReader fs = new FastReader();
        out = new PrintWriter(new BufferedOutputStream(System.out));

       int n = fs.nextInt();
       int[] inp = new int[n];

       for(int i=0 ; i<n ; i++){
           inp[i] = fs.nextInt();
       }

       long ans = 0 ;

       for(int i=0 ; i<n ; i++){
           int max = inp[i];
           for(int j=i+1 ; j<n ; j++){
               if(inp[j]<max){
                   ans += (max-inp[j]);
               }else{
                   i = j - 1 ;
                   break;
               }
               if(j==n-1){
                   i = j;
               }
           }
       }

       out.println(ans);

        out.close();

    }

    //-----------PrintWriter for faster output---------------------------------
    public static PrintWriter out;

    //-----------MyScanner class for faster input----------
    public 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;
        }

    }
    //--------------------------------------------------------
}

