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

public class Main {

    public static void main(String[] args) {
        MyScanner scn = new MyScanner();
        out = new PrintWriter(new BufferedOutputStream(System.out));

        // Start writing your solution here. -------------------------------------

        /*
         * int n = sc.nextInt(); // read input as integer long k = sc.nextLong(); //
         * read input as long double d = sc.nextDouble(); // read input as double String
         * str = sc.next(); // read input as String String s = sc.nextLine(); // read
         * whole line as String
         * 
         * int result = 3*n; out.println(result); // print via PrintWriter
         */

        // Stop writing your solution here. -------------------------------------

        int n = scn.nextInt();
        long[] arr = new long[n];
        for (int i = 0; i < n; i++)
            arr[i] = scn.nextLong();

        long[] check = new long[n];
        check[0] = arr[0];

        long stool = 0;
        for (int i = 1; i < arr.length; i++) {
            if (arr[i] >= check[i - 1]) {
                check[i] = arr[i];

            } else {
                check[i] = check[i - 1];
                stool += check[i] - arr[i];
            }
        }
        out.println(stool);
        out.close();
    }

    public static PrintWriter out;

    public static class MyScanner {
        BufferedReader br;
        StringTokenizer st;

        public MyScanner() {
            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.util.*; util.* java import java.io.*; io.* java public class Main {

    public static void main(String[] args) {
        MyScanner scn = new MyScanner();
        out = new PrintWriter(new BufferedOutputStream(System.out));

        // Start writing your solution here. -------------------------------------

        /*
         * int n = sc.nextInt(); // read input as integer long k = sc.nextLong(); //
         * read input as long double d = sc.nextDouble(); // read input as double String
         * str = sc.next(); // read input as String String s = sc.nextLine(); // read
         * whole line as String
         * 
         * int result = 3*n; out.println(result); // print via PrintWriter
         */

        // Stop writing your solution here. -------------------------------------

        int n = scn.nextInt();
        long[] arr = new long[n];
        for (int i = 0; i < n; i++)
            arr[i] = scn.nextLong();

        long[] check = new long[n];
        check[0] = arr[0];

        long stool = 0;
        for (int i = 1; i < arr.length; i++) {
            if (arr[i] >= check[i - 1]) {
                check[i] = arr[i];

            } else {
                check[i] = check[i - 1];
                stool += check[i] - arr[i];
            }
        }
        out.println(stool);
        out.close();
    }

    public static PrintWriter out;

    public static class MyScanner {
        BufferedReader br;
        StringTokenizer st;

        public MyScanner() {
            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 public static PrintWriter out; out public static void main(String[] args) {
        MyScanner scn = new MyScanner();
        out = new PrintWriter(new BufferedOutputStream(System.out));

        // Start writing your solution here. -------------------------------------

        /*
         * int n = sc.nextInt(); // read input as integer long k = sc.nextLong(); //
         * read input as long double d = sc.nextDouble(); // read input as double String
         * str = sc.next(); // read input as String String s = sc.nextLine(); // read
         * whole line as String
         * 
         * int result = 3*n; out.println(result); // print via PrintWriter
         */

        // Stop writing your solution here. -------------------------------------

        int n = scn.nextInt();
        long[] arr = new long[n];
        for (int i = 0; i < n; i++)
            arr[i] = scn.nextLong();

        long[] check = new long[n];
        check[0] = arr[0];

        long stool = 0;
        for (int i = 1; i < arr.length; i++) {
            if (arr[i] >= check[i - 1]) {
                check[i] = arr[i];

            } else {
                check[i] = check[i - 1];
                stool += check[i] - arr[i];
            }
        }
        out.println(stool);
        out.close();
    } main {
        MyScanner scn = new MyScanner();
        out = new PrintWriter(new BufferedOutputStream(System.out));

        // Start writing your solution here. -------------------------------------

        /*
         * int n = sc.nextInt(); // read input as integer long k = sc.nextLong(); //
         * read input as long double d = sc.nextDouble(); // read input as double String
         * str = sc.next(); // read input as String String s = sc.nextLine(); // read
         * whole line as String
         * 
         * int result = 3*n; out.println(result); // print via PrintWriter
         */

        // Stop writing your solution here. -------------------------------------

        int n = scn.nextInt();
        long[] arr = new long[n];
        for (int i = 0; i < n; i++)
            arr[i] = scn.nextLong();

        long[] check = new long[n];
        check[0] = arr[0];

        long stool = 0;
        for (int i = 1; i < arr.length; i++) {
            if (arr[i] >= check[i - 1]) {
                check[i] = arr[i];

            } else {
                check[i] = check[i - 1];
                stool += check[i] - arr[i];
            }
        }
        out.println(stool);
        out.close();
    } MyScanner scn = new MyScanner(); scn new MyScanner() out = new PrintWriter(new BufferedOutputStream(System.out)) out new PrintWriter(new BufferedOutputStream(System.out)) int n = scn.nextInt(); n scn.nextInt() scn.nextInt scn long[] arr = new long[n]; arr new long[n] n for (int i = 0; i < n; i++)
            arr[i] = scn.nextLong(); int i = 0; int i = 0; i 0 i < n i n i++ i++ i arr[i] = scn.nextLong(); arr[i] = scn.nextLong() arr[i] arr i scn.nextLong() scn.nextLong scn long[] check = new long[n]; check new long[n] n check[0] = arr[0] check[0] check 0 arr[0] arr 0 long stool = 0; stool 0 for (int i = 1; i < arr.length; i++) {
            if (arr[i] >= check[i - 1]) {
                check[i] = arr[i];

            } else {
                check[i] = check[i - 1];
                stool += check[i] - arr[i];
            }
        } int i = 1; int i = 1; i 1 i < arr.length i arr.length arr arr.length i++ i++ i {
            if (arr[i] >= check[i - 1]) {
                check[i] = arr[i];

            } else {
                check[i] = check[i - 1];
                stool += check[i] - arr[i];
            }
        } {
            if (arr[i] >= check[i - 1]) {
                check[i] = arr[i];

            } else {
                check[i] = check[i - 1];
                stool += check[i] - arr[i];
            }
        } if (arr[i] >= check[i - 1]) {
                check[i] = arr[i];

            } else {
                check[i] = check[i - 1];
                stool += check[i] - arr[i];
            } arr[i] >= check[i - 1] arr[i] arr i check[i - 1] check i - 1 i 1 {
                check[i] = arr[i];

            } check[i] = arr[i] check[i] check i arr[i] arr i {
                check[i] = check[i - 1];
                stool += check[i] - arr[i];
            } check[i] = check[i - 1] check[i] check i check[i - 1] check i - 1 i 1 stool += check[i] - arr[i] stool check[i] - arr[i] check[i] check i arr[i] arr i out.println(stool) out.println out stool out.close() out.close out String[] args args public static class MyScanner {
        BufferedReader br;
        StringTokenizer st;

        public MyScanner() {
            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;
        }

    } MyScanner BufferedReader br; br StringTokenizer st; st public MyScanner() {
            br = new BufferedReader(new InputStreamReader(System.in));
        } MyScanner {
            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) {
        MyScanner scn = new MyScanner();
        out = new PrintWriter(new BufferedOutputStream(System.out));

        // Start writing your solution here. -------------------------------------

        /*
         * int n = sc.nextInt(); // read input as integer long k = sc.nextLong(); //
         * read input as long double d = sc.nextDouble(); // read input as double String
         * str = sc.next(); // read input as String String s = sc.nextLine(); // read
         * whole line as String
         * 
         * int result = 3*n; out.println(result); // print via PrintWriter
         */

        // Stop writing your solution here. -------------------------------------

        int n = scn.nextInt();
        long[] arr = new long[n];
        for (int i = 0; i < n; i++)
            arr[i] = scn.nextLong();

        long[] check = new long[n];
        check[0] = arr[0];

        long stool = 0;
        for (int i = 1; i < arr.length; i++) {
            if (arr[i] >= check[i - 1]) {
                check[i] = arr[i];

            } else {
                check[i] = check[i - 1];
                stool += check[i] - arr[i];
            }
        }
        out.println(stool);
        out.close();
    }

    public static PrintWriter out;

    public static class MyScanner {
        BufferedReader br;
        StringTokenizer st;

        public MyScanner() {
            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) {
        MyScanner scn = new MyScanner();
        out = new PrintWriter(new BufferedOutputStream(System.out));

        // Start writing your solution here. -------------------------------------

        /*
         * int n = sc.nextInt(); // read input as integer long k = sc.nextLong(); //
         * read input as long double d = sc.nextDouble(); // read input as double String
         * str = sc.next(); // read input as String String s = sc.nextLine(); // read
         * whole line as String
         * 
         * int result = 3*n; out.println(result); // print via PrintWriter
         */

        // Stop writing your solution here. -------------------------------------

        int n = scn.nextInt();
        long[] arr = new long[n];
        for (int i = 0; i < n; i++)
            arr[i] = scn.nextLong();

        long[] check = new long[n];
        check[0] = arr[0];

        long stool = 0;
        for (int i = 1; i < arr.length; i++) {
            if (arr[i] >= check[i - 1]) {
                check[i] = arr[i];

            } else {
                check[i] = check[i - 1];
                stool += check[i] - arr[i];
            }
        }
        out.println(stool);
        out.close();
    }

    public static PrintWriter out;

    public static class MyScanner {
        BufferedReader br;
        StringTokenizer st;

        public MyScanner() {
            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.util.*;
import java.io.*;

public class Main {

    public static void main(String[] args) {
        MyScanner scn = new MyScanner();
        out = new PrintWriter(new BufferedOutputStream(System.out));

        // Start writing your solution here. -------------------------------------

        /*
         * int n = sc.nextInt(); // read input as integer long k = sc.nextLong(); //
         * read input as long double d = sc.nextDouble(); // read input as double String
         * str = sc.next(); // read input as String String s = sc.nextLine(); // read
         * whole line as String
         * 
         * int result = 3*n; out.println(result); // print via PrintWriter
         */

        // Stop writing your solution here. -------------------------------------

        int n = scn.nextInt();
        long[] arr = new long[n];
        for (int i = 0; i < n; i++)
            arr[i] = scn.nextLong();

        long[] check = new long[n];
        check[0] = arr[0];

        long stool = 0;
        for (int i = 1; i < arr.length; i++) {
            if (arr[i] >= check[i - 1]) {
                check[i] = arr[i];

            } else {
                check[i] = check[i - 1];
                stool += check[i] - arr[i];
            }
        }
        out.println(stool);
        out.close();
    }

    public static PrintWriter out;

    public static class MyScanner {
        BufferedReader br;
        StringTokenizer st;

        public MyScanner() {
            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;
        }

    }

}