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

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());
        }

        String nextLine()
        {
            String str = "";

            try
            {
                str = br.readLine();
            }
            catch(IOException e)
            {
                e.printStackTrace();
            }
            return str;
        }
    }

    static class Reader
    {
        final private int BUFFER_SIZE = 1 << 16;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer, bytesRead;

        public Reader()
        {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public Reader(String file_name) throws IOException
        {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public String readLine() throws IOException
        {
            byte[] buf = new byte[64]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1)
            {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        }

        public int nextInt() throws IOException
        {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        }

        public long nextLong() throws IOException
        {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }

        public double nextDouble() throws IOException
        {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();

            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');

            if (c == '.')
            {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg)
                return -ret;
            return ret;
        }

        private void fillBuffer() throws IOException
        {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        }

        private byte read() throws IOException
        {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        }

        public void close() throws IOException
        {
            if (din == null)
                return;
            din.close();
        }
    }

    public static void main(String[] args) throws java.lang.Exception
    {
        try
        {
            //FastReader fr = new FastReader();
            Reader fr = new Reader();
            PrintWriter out = new PrintWriter(System.out);

            int n = fr.nextInt();
            List<Long> list = new ArrayList<>();
            for (int i=0;i<n;i++) list.add(fr.nextLong());

            long sum = 0;

            for (int i=1;i<n;i++)
            {
                if (list.get(i)<list.get(i-1))
                {
                    sum+=list.get(i-1)-list.get(i);

                    list.set(i,list.get(i)+list.get(i-1)-list.get(i));
                }
            }

            out.println(sum);

            out.flush();
            out.close();
        }

        catch(Exception e){e.printStackTrace();}
        finally{}
    }
} import java.util.*; util.* java import java.io.*; io.* 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());
        }

        String nextLine()
        {
            String str = "";

            try
            {
                str = br.readLine();
            }
            catch(IOException e)
            {
                e.printStackTrace();
            }
            return str;
        }
    }

    static class Reader
    {
        final private int BUFFER_SIZE = 1 << 16;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer, bytesRead;

        public Reader()
        {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public Reader(String file_name) throws IOException
        {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public String readLine() throws IOException
        {
            byte[] buf = new byte[64]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1)
            {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        }

        public int nextInt() throws IOException
        {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        }

        public long nextLong() throws IOException
        {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }

        public double nextDouble() throws IOException
        {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();

            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');

            if (c == '.')
            {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg)
                return -ret;
            return ret;
        }

        private void fillBuffer() throws IOException
        {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        }

        private byte read() throws IOException
        {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        }

        public void close() throws IOException
        {
            if (din == null)
                return;
            din.close();
        }
    }

    public static void main(String[] args) throws java.lang.Exception
    {
        try
        {
            //FastReader fr = new FastReader();
            Reader fr = new Reader();
            PrintWriter out = new PrintWriter(System.out);

            int n = fr.nextInt();
            List<Long> list = new ArrayList<>();
            for (int i=0;i<n;i++) list.add(fr.nextLong());

            long sum = 0;

            for (int i=1;i<n;i++)
            {
                if (list.get(i)<list.get(i-1))
                {
                    sum+=list.get(i-1)-list.get(i);

                    list.set(i,list.get(i)+list.get(i-1)-list.get(i));
                }
            }

            out.println(sum);

            out.flush();
            out.close();
        }

        catch(Exception e){e.printStackTrace();}
        finally{}
    }
} Main public static void main(String[] args) throws java.lang.Exception
    {
        try
        {
            //FastReader fr = new FastReader();
            Reader fr = new Reader();
            PrintWriter out = new PrintWriter(System.out);

            int n = fr.nextInt();
            List<Long> list = new ArrayList<>();
            for (int i=0;i<n;i++) list.add(fr.nextLong());

            long sum = 0;

            for (int i=1;i<n;i++)
            {
                if (list.get(i)<list.get(i-1))
                {
                    sum+=list.get(i-1)-list.get(i);

                    list.set(i,list.get(i)+list.get(i-1)-list.get(i));
                }
            }

            out.println(sum);

            out.flush();
            out.close();
        }

        catch(Exception e){e.printStackTrace();}
        finally{}
    } main {
        try
        {
            //FastReader fr = new FastReader();
            Reader fr = new Reader();
            PrintWriter out = new PrintWriter(System.out);

            int n = fr.nextInt();
            List<Long> list = new ArrayList<>();
            for (int i=0;i<n;i++) list.add(fr.nextLong());

            long sum = 0;

            for (int i=1;i<n;i++)
            {
                if (list.get(i)<list.get(i-1))
                {
                    sum+=list.get(i-1)-list.get(i);

                    list.set(i,list.get(i)+list.get(i-1)-list.get(i));
                }
            }

            out.println(sum);

            out.flush();
            out.close();
        }

        catch(Exception e){e.printStackTrace();}
        finally{}
    } try
        {
            //FastReader fr = new FastReader();
            Reader fr = new Reader();
            PrintWriter out = new PrintWriter(System.out);

            int n = fr.nextInt();
            List<Long> list = new ArrayList<>();
            for (int i=0;i<n;i++) list.add(fr.nextLong());

            long sum = 0;

            for (int i=1;i<n;i++)
            {
                if (list.get(i)<list.get(i-1))
                {
                    sum+=list.get(i-1)-list.get(i);

                    list.set(i,list.get(i)+list.get(i-1)-list.get(i));
                }
            }

            out.println(sum);

            out.flush();
            out.close();
        }

        catch(Exception e){e.printStackTrace();}
        finally{} catch(Exception e){e.printStackTrace();} Exception e {e.printStackTrace();} e.printStackTrace() e.printStackTrace e {} {
            //FastReader fr = new FastReader();
            Reader fr = new Reader();
            PrintWriter out = new PrintWriter(System.out);

            int n = fr.nextInt();
            List<Long> list = new ArrayList<>();
            for (int i=0;i<n;i++) list.add(fr.nextLong());

            long sum = 0;

            for (int i=1;i<n;i++)
            {
                if (list.get(i)<list.get(i-1))
                {
                    sum+=list.get(i-1)-list.get(i);

                    list.set(i,list.get(i)+list.get(i-1)-list.get(i));
                }
            }

            out.println(sum);

            out.flush();
            out.close();
        } Reader fr = new Reader(); fr new Reader() PrintWriter out = new PrintWriter(System.out); out new PrintWriter(System.out) int n = fr.nextInt(); n fr.nextInt() fr.nextInt fr List<Long> list = new ArrayList<>(); list new ArrayList<>() for (int i=0;i<n;i++) list.add(fr.nextLong()); int i=0; int i=0; i 0 i<n i n i++ i++ i list.add(fr.nextLong()); list.add(fr.nextLong()) list.add list fr.nextLong() fr.nextLong fr long sum = 0; sum 0 for (int i=1;i<n;i++)
            {
                if (list.get(i)<list.get(i-1))
                {
                    sum+=list.get(i-1)-list.get(i);

                    list.set(i,list.get(i)+list.get(i-1)-list.get(i));
                }
            } int i=1; int i=1; i 1 i<n i n i++ i++ i {
                if (list.get(i)<list.get(i-1))
                {
                    sum+=list.get(i-1)-list.get(i);

                    list.set(i,list.get(i)+list.get(i-1)-list.get(i));
                }
            } {
                if (list.get(i)<list.get(i-1))
                {
                    sum+=list.get(i-1)-list.get(i);

                    list.set(i,list.get(i)+list.get(i-1)-list.get(i));
                }
            } if (list.get(i)<list.get(i-1))
                {
                    sum+=list.get(i-1)-list.get(i);

                    list.set(i,list.get(i)+list.get(i-1)-list.get(i));
                } list.get(i)<list.get(i-1) list.get(i) list.get list i list.get(i-1) list.get list i-1 i 1 {
                    sum+=list.get(i-1)-list.get(i);

                    list.set(i,list.get(i)+list.get(i-1)-list.get(i));
                } sum+=list.get(i-1)-list.get(i) sum list.get(i-1)-list.get(i) list.get(i-1) list.get list i-1 i 1 list.get(i) list.get list i list.set(i,list.get(i)+list.get(i-1)-list.get(i)) list.set list i list.get(i)+list.get(i-1)-list.get(i) list.get(i)+list.get(i-1) list.get(i) list.get list i list.get(i-1) list.get list i-1 i 1 list.get(i) list.get list i out.println(sum) out.println out sum out.flush() out.flush out out.close() out.close out 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());
        }

        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 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 static class Reader
    {
        final private int BUFFER_SIZE = 1 << 16;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer, bytesRead;

        public Reader()
        {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public Reader(String file_name) throws IOException
        {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public String readLine() throws IOException
        {
            byte[] buf = new byte[64]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1)
            {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        }

        public int nextInt() throws IOException
        {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        }

        public long nextLong() throws IOException
        {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }

        public double nextDouble() throws IOException
        {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();

            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');

            if (c == '.')
            {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg)
                return -ret;
            return ret;
        }

        private void fillBuffer() throws IOException
        {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        }

        private byte read() throws IOException
        {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        }

        public void close() throws IOException
        {
            if (din == null)
                return;
            din.close();
        }
    } Reader final private int BUFFER_SIZE = 1 << 16; BUFFER_SIZE 1 << 16 1 16 private DataInputStream din; din private byte[] buffer; buffer private int bufferPointer bufferPointer bytesRead; bytesRead public Reader()
        {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        } Reader {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        } din = new DataInputStream(System.in) din new DataInputStream(System.in) buffer = new byte[BUFFER_SIZE] buffer new byte[BUFFER_SIZE] BUFFER_SIZE bufferPointer = bytesRead = 0 bufferPointer bytesRead = 0 bytesRead 0 public Reader(String file_name) throws IOException
        {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        } Reader {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        } din = new DataInputStream(new FileInputStream(file_name)) din new DataInputStream(new FileInputStream(file_name)) buffer = new byte[BUFFER_SIZE] buffer new byte[BUFFER_SIZE] BUFFER_SIZE bufferPointer = bytesRead = 0 bufferPointer bytesRead = 0 bytesRead 0 String file_name file_name public String readLine() throws IOException
        {
            byte[] buf = new byte[64]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1)
            {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        } readLine {
            byte[] buf = new byte[64]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1)
            {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        } byte[] buf = new byte[64]; buf new byte[64] 64 int cnt = 0 cnt 0 c; c while ((c = read()) != -1)
            {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            } (c = read()) != -1 (c = read()) c read() read -1 1 {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            } if (c == '\n')
                    break; c == '\n' c '\n' break; buf[cnt++] = (byte) c buf[cnt++] buf cnt++ cnt (byte) c return new String(buf, 0, cnt); new String(buf, 0, cnt) public int nextInt() throws IOException
        {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        } nextInt {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        } int ret = 0; ret 0 byte c = read(); c read() read while (c <= ' ')
                c = read(); c <= ' ' c ' ' c = read() c read() read boolean neg = (c == '-'); neg (c == '-') c '-' if (neg)
                c = read(); neg c = read() c read() read do
            {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9'); (c = read()) >= '0' && c <= '9' (c = read()) >= '0' (c = read()) c read() read '0' c <= '9' c '9' {
                ret = ret * 10 + c - '0';
            } ret = ret * 10 + c - '0' ret ret * 10 + c - '0' ret * 10 + c ret * 10 ret 10 c '0' if (neg)
                return -ret; neg return -ret; -ret ret return ret; ret public long nextLong() throws IOException
        {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        } nextLong {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        } long ret = 0; ret 0 byte c = read(); c read() read while (c <= ' ')
                c = read(); c <= ' ' c ' ' c = read() c read() read boolean neg = (c == '-'); neg (c == '-') c '-' if (neg)
                c = read(); neg c = read() c read() read do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9'); (c = read()) >= '0' && c <= '9' (c = read()) >= '0' (c = read()) c read() read '0' c <= '9' c '9' {
                ret = ret * 10 + c - '0';
            } ret = ret * 10 + c - '0' ret ret * 10 + c - '0' ret * 10 + c ret * 10 ret 10 c '0' if (neg)
                return -ret; neg return -ret; -ret ret return ret; ret public double nextDouble() throws IOException
        {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();

            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');

            if (c == '.')
            {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg)
                return -ret;
            return ret;
        } nextDouble {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();

            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');

            if (c == '.')
            {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg)
                return -ret;
            return ret;
        } double ret = 0 ret 0 div = 1; div 1 byte c = read(); c read() read while (c <= ' ')
                c = read(); c <= ' ' c ' ' c = read() c read() read boolean neg = (c == '-'); neg (c == '-') c '-' if (neg)
                c = read(); neg c = read() c read() read do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9'); (c = read()) >= '0' && c <= '9' (c = read()) >= '0' (c = read()) c read() read '0' c <= '9' c '9' {
                ret = ret * 10 + c - '0';
            } ret = ret * 10 + c - '0' ret ret * 10 + c - '0' ret * 10 + c ret * 10 ret 10 c '0' if (c == '.')
            {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            } c == '.' c '.' {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            } while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                } (c = read()) >= '0' && c <= '9' (c = read()) >= '0' (c = read()) c read() read '0' c <= '9' c '9' {
                    ret += (c - '0') / (div *= 10);
                } ret += (c - '0') / (div *= 10) ret (c - '0') / (div *= 10) (c - '0') c '0' (div *= 10) div 10 if (neg)
                return -ret; neg return -ret; -ret ret return ret; ret private void fillBuffer() throws IOException
        {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        } fillBuffer {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        } bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE) bytesRead din.read(buffer, bufferPointer = 0, BUFFER_SIZE) din.read din buffer bufferPointer = 0 bufferPointer 0 BUFFER_SIZE if (bytesRead == -1)
                buffer[0] = -1; bytesRead == -1 bytesRead -1 1 buffer[0] = -1 buffer[0] buffer 0 -1 1 private byte read() throws IOException
        {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        } read {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        } if (bufferPointer == bytesRead)
                fillBuffer(); bufferPointer == bytesRead bufferPointer bytesRead fillBuffer() fillBuffer return buffer[bufferPointer++]; buffer[bufferPointer++] buffer bufferPointer++ bufferPointer public void close() throws IOException
        {
            if (din == null)
                return;
            din.close();
        } close {
            if (din == null)
                return;
            din.close();
        } if (din == null)
                return; din == null din null return; din.close() din.close din 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());
        }

        String nextLine()
        {
            String str = "";

            try
            {
                str = br.readLine();
            }
            catch(IOException e)
            {
                e.printStackTrace();
            }
            return str;
        }
    }

    static class Reader
    {
        final private int BUFFER_SIZE = 1 << 16;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer, bytesRead;

        public Reader()
        {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public Reader(String file_name) throws IOException
        {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public String readLine() throws IOException
        {
            byte[] buf = new byte[64]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1)
            {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        }

        public int nextInt() throws IOException
        {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        }

        public long nextLong() throws IOException
        {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }

        public double nextDouble() throws IOException
        {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();

            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');

            if (c == '.')
            {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg)
                return -ret;
            return ret;
        }

        private void fillBuffer() throws IOException
        {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        }

        private byte read() throws IOException
        {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        }

        public void close() throws IOException
        {
            if (din == null)
                return;
            din.close();
        }
    }

    public static void main(String[] args) throws java.lang.Exception
    {
        try
        {
            //FastReader fr = new FastReader();
            Reader fr = new Reader();
            PrintWriter out = new PrintWriter(System.out);

            int n = fr.nextInt();
            List<Long> list = new ArrayList<>();
            for (int i=0;i<n;i++) list.add(fr.nextLong());

            long sum = 0;

            for (int i=1;i<n;i++)
            {
                if (list.get(i)<list.get(i-1))
                {
                    sum+=list.get(i-1)-list.get(i);

                    list.set(i,list.get(i)+list.get(i-1)-list.get(i));
                }
            }

            out.println(sum);

            out.flush();
            out.close();
        }

        catch(Exception e){e.printStackTrace();}
        finally{}
    }
} 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());
        }

        String nextLine()
        {
            String str = "";

            try
            {
                str = br.readLine();
            }
            catch(IOException e)
            {
                e.printStackTrace();
            }
            return str;
        }
    }

    static class Reader
    {
        final private int BUFFER_SIZE = 1 << 16;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer, bytesRead;

        public Reader()
        {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public Reader(String file_name) throws IOException
        {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public String readLine() throws IOException
        {
            byte[] buf = new byte[64]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1)
            {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        }

        public int nextInt() throws IOException
        {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        }

        public long nextLong() throws IOException
        {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }

        public double nextDouble() throws IOException
        {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();

            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');

            if (c == '.')
            {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg)
                return -ret;
            return ret;
        }

        private void fillBuffer() throws IOException
        {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        }

        private byte read() throws IOException
        {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        }

        public void close() throws IOException
        {
            if (din == null)
                return;
            din.close();
        }
    }

    public static void main(String[] args) throws java.lang.Exception
    {
        try
        {
            //FastReader fr = new FastReader();
            Reader fr = new Reader();
            PrintWriter out = new PrintWriter(System.out);

            int n = fr.nextInt();
            List<Long> list = new ArrayList<>();
            for (int i=0;i<n;i++) list.add(fr.nextLong());

            long sum = 0;

            for (int i=1;i<n;i++)
            {
                if (list.get(i)<list.get(i-1))
                {
                    sum+=list.get(i-1)-list.get(i);

                    list.set(i,list.get(i)+list.get(i-1)-list.get(i));
                }
            }

            out.println(sum);

            out.flush();
            out.close();
        }

        catch(Exception e){e.printStackTrace();}
        finally{}
    }
} Main
import java.util.*;
import java.io.*;

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());
        }

        String nextLine()
        {
            String str = "";

            try
            {
                str = br.readLine();
            }
            catch(IOException e)
            {
                e.printStackTrace();
            }
            return str;
        }
    }

    static class Reader
    {
        final private int BUFFER_SIZE = 1 << 16;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer, bytesRead;

        public Reader()
        {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public Reader(String file_name) throws IOException
        {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public String readLine() throws IOException
        {
            byte[] buf = new byte[64]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1)
            {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        }

        public int nextInt() throws IOException
        {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        }

        public long nextLong() throws IOException
        {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }

        public double nextDouble() throws IOException
        {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();

            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');

            if (c == '.')
            {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg)
                return -ret;
            return ret;
        }

        private void fillBuffer() throws IOException
        {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        }

        private byte read() throws IOException
        {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        }

        public void close() throws IOException
        {
            if (din == null)
                return;
            din.close();
        }
    }

    public static void main(String[] args) throws java.lang.Exception
    {
        try
        {
            //FastReader fr = new FastReader();
            Reader fr = new Reader();
            PrintWriter out = new PrintWriter(System.out);

            int n = fr.nextInt();
            List<Long> list = new ArrayList<>();
            for (int i=0;i<n;i++) list.add(fr.nextLong());

            long sum = 0;

            for (int i=1;i<n;i++)
            {
                if (list.get(i)<list.get(i-1))
                {
                    sum+=list.get(i-1)-list.get(i);

                    list.set(i,list.get(i)+list.get(i-1)-list.get(i));
                }
            }

            out.println(sum);

            out.flush();
            out.close();
        }

        catch(Exception e){e.printStackTrace();}
        finally{}
    }
}
