import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main
{
    public static void main(String[] args)
    {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskC solver = new TaskC();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskC
    {
        public void solve(int testNumber, Scanner in, PrintWriter out)
        {
            int T = 1;
            while (T-- > 0)
            {
                solveOne(in, out);
            }
        }

        private void solveOne(Scanner in, PrintWriter out)
        {
            int N = in.nextInt();
            int H[] = CPUtils.readIntArray(N, in);

            long ans = 0;
            for (int i = 1; i < N; i++)
            {
                if (H[i - 1] > H[i])
                {
                    ans += H[i - 1] - H[i];
                    H[i] = H[i - 1];
                }
            }
            out.println(ans);
        }

    }

    static class CPUtils
    {
        public static int[] readIntArray(int size, Scanner in)
        {
            int[] array = new int[size];
            for (int i = 0; i < size; i++)
            {
                array[i] = in.nextInt();
            }
            return array;
        }

    }
}
 import java.io.OutputStream; OutputStream java.io import java.io.IOException; IOException java.io import java.io.InputStream; InputStream java.io import java.io.PrintWriter; PrintWriter java.io import java.util.Scanner; Scanner java.util public class Main
{
    public static void main(String[] args)
    {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskC solver = new TaskC();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskC
    {
        public void solve(int testNumber, Scanner in, PrintWriter out)
        {
            int T = 1;
            while (T-- > 0)
            {
                solveOne(in, out);
            }
        }

        private void solveOne(Scanner in, PrintWriter out)
        {
            int N = in.nextInt();
            int H[] = CPUtils.readIntArray(N, in);

            long ans = 0;
            for (int i = 1; i < N; i++)
            {
                if (H[i - 1] > H[i])
                {
                    ans += H[i - 1] - H[i];
                    H[i] = H[i - 1];
                }
            }
            out.println(ans);
        }

    }

    static class CPUtils
    {
        public static int[] readIntArray(int size, Scanner in)
        {
            int[] array = new int[size];
            for (int i = 0; i < size; i++)
            {
                array[i] = in.nextInt();
            }
            return array;
        }

    }
} Main public static void main(String[] args)
    {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskC solver = new TaskC();
        solver.solve(1, in, out);
        out.close();
    } main {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskC solver = new TaskC();
        solver.solve(1, in, out);
        out.close();
    } InputStream inputStream = System.in; inputStream System.in System System.in OutputStream outputStream = System.out; outputStream System.out System System.out Scanner in = new Scanner(inputStream); in new Scanner(inputStream) PrintWriter out = new PrintWriter(outputStream); out new PrintWriter(outputStream) TaskC solver = new TaskC(); solver new TaskC() solver.solve(1, in, out) solver.solve solver 1 in out out.close() out.close out String[] args args static class TaskC
    {
        public void solve(int testNumber, Scanner in, PrintWriter out)
        {
            int T = 1;
            while (T-- > 0)
            {
                solveOne(in, out);
            }
        }

        private void solveOne(Scanner in, PrintWriter out)
        {
            int N = in.nextInt();
            int H[] = CPUtils.readIntArray(N, in);

            long ans = 0;
            for (int i = 1; i < N; i++)
            {
                if (H[i - 1] > H[i])
                {
                    ans += H[i - 1] - H[i];
                    H[i] = H[i - 1];
                }
            }
            out.println(ans);
        }

    } TaskC public void solve(int testNumber, Scanner in, PrintWriter out)
        {
            int T = 1;
            while (T-- > 0)
            {
                solveOne(in, out);
            }
        } solve {
            int T = 1;
            while (T-- > 0)
            {
                solveOne(in, out);
            }
        } int T = 1; T 1 while (T-- > 0)
            {
                solveOne(in, out);
            } T-- > 0 T-- T 0 {
                solveOne(in, out);
            } solveOne(in, out) solveOne in out int testNumber testNumber Scanner in in PrintWriter out out private void solveOne(Scanner in, PrintWriter out)
        {
            int N = in.nextInt();
            int H[] = CPUtils.readIntArray(N, in);

            long ans = 0;
            for (int i = 1; i < N; i++)
            {
                if (H[i - 1] > H[i])
                {
                    ans += H[i - 1] - H[i];
                    H[i] = H[i - 1];
                }
            }
            out.println(ans);
        } solveOne {
            int N = in.nextInt();
            int H[] = CPUtils.readIntArray(N, in);

            long ans = 0;
            for (int i = 1; i < N; i++)
            {
                if (H[i - 1] > H[i])
                {
                    ans += H[i - 1] - H[i];
                    H[i] = H[i - 1];
                }
            }
            out.println(ans);
        } int N = in.nextInt(); N in.nextInt() in.nextInt in int H[] = CPUtils.readIntArray(N, in); H CPUtils.readIntArray(N, in) CPUtils.readIntArray CPUtils N in long ans = 0; ans 0 for (int i = 1; i < N; i++)
            {
                if (H[i - 1] > H[i])
                {
                    ans += H[i - 1] - H[i];
                    H[i] = H[i - 1];
                }
            } int i = 1; int i = 1; i 1 i < N i N i++ i++ i {
                if (H[i - 1] > H[i])
                {
                    ans += H[i - 1] - H[i];
                    H[i] = H[i - 1];
                }
            } {
                if (H[i - 1] > H[i])
                {
                    ans += H[i - 1] - H[i];
                    H[i] = H[i - 1];
                }
            } if (H[i - 1] > H[i])
                {
                    ans += H[i - 1] - H[i];
                    H[i] = H[i - 1];
                } H[i - 1] > H[i] H[i - 1] H i - 1 i 1 H[i] H i {
                    ans += H[i - 1] - H[i];
                    H[i] = H[i - 1];
                } ans += H[i - 1] - H[i] ans H[i - 1] - H[i] H[i - 1] H i - 1 i 1 H[i] H i H[i] = H[i - 1] H[i] H i H[i - 1] H i - 1 i 1 out.println(ans) out.println out ans Scanner in in PrintWriter out out static class CPUtils
    {
        public static int[] readIntArray(int size, Scanner in)
        {
            int[] array = new int[size];
            for (int i = 0; i < size; i++)
            {
                array[i] = in.nextInt();
            }
            return array;
        }

    } CPUtils public static int[] readIntArray(int size, Scanner in)
        {
            int[] array = new int[size];
            for (int i = 0; i < size; i++)
            {
                array[i] = in.nextInt();
            }
            return array;
        } readIntArray {
            int[] array = new int[size];
            for (int i = 0; i < size; i++)
            {
                array[i] = in.nextInt();
            }
            return array;
        } int[] array = new int[size]; array new int[size] size for (int i = 0; i < size; i++)
            {
                array[i] = in.nextInt();
            } int i = 0; int i = 0; i 0 i < size i size i++ i++ i {
                array[i] = in.nextInt();
            } {
                array[i] = in.nextInt();
            } array[i] = in.nextInt() array[i] array i in.nextInt() in.nextInt in return array; array int size size Scanner in in public class Main
{
    public static void main(String[] args)
    {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskC solver = new TaskC();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskC
    {
        public void solve(int testNumber, Scanner in, PrintWriter out)
        {
            int T = 1;
            while (T-- > 0)
            {
                solveOne(in, out);
            }
        }

        private void solveOne(Scanner in, PrintWriter out)
        {
            int N = in.nextInt();
            int H[] = CPUtils.readIntArray(N, in);

            long ans = 0;
            for (int i = 1; i < N; i++)
            {
                if (H[i - 1] > H[i])
                {
                    ans += H[i - 1] - H[i];
                    H[i] = H[i - 1];
                }
            }
            out.println(ans);
        }

    }

    static class CPUtils
    {
        public static int[] readIntArray(int size, Scanner in)
        {
            int[] array = new int[size];
            for (int i = 0; i < size; i++)
            {
                array[i] = in.nextInt();
            }
            return array;
        }

    }
} public class Main
{
    public static void main(String[] args)
    {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskC solver = new TaskC();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskC
    {
        public void solve(int testNumber, Scanner in, PrintWriter out)
        {
            int T = 1;
            while (T-- > 0)
            {
                solveOne(in, out);
            }
        }

        private void solveOne(Scanner in, PrintWriter out)
        {
            int N = in.nextInt();
            int H[] = CPUtils.readIntArray(N, in);

            long ans = 0;
            for (int i = 1; i < N; i++)
            {
                if (H[i - 1] > H[i])
                {
                    ans += H[i - 1] - H[i];
                    H[i] = H[i - 1];
                }
            }
            out.println(ans);
        }

    }

    static class CPUtils
    {
        public static int[] readIntArray(int size, Scanner in)
        {
            int[] array = new int[size];
            for (int i = 0; i < size; i++)
            {
                array[i] = in.nextInt();
            }
            return array;
        }

    }
} Main
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class Main
{
    public static void main(String[] args)
    {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskC solver = new TaskC();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskC
    {
        public void solve(int testNumber, Scanner in, PrintWriter out)
        {
            int T = 1;
            while (T-- > 0)
            {
                solveOne(in, out);
            }
        }

        private void solveOne(Scanner in, PrintWriter out)
        {
            int N = in.nextInt();
            int H[] = CPUtils.readIntArray(N, in);

            long ans = 0;
            for (int i = 1; i < N; i++)
            {
                if (H[i - 1] > H[i])
                {
                    ans += H[i - 1] - H[i];
                    H[i] = H[i - 1];
                }
            }
            out.println(ans);
        }

    }

    static class CPUtils
    {
        public static int[] readIntArray(int size, Scanner in)
        {
            int[] array = new int[size];
            for (int i = 0; i < size; i++)
            {
                array[i] = in.nextInt();
            }
            return array;
        }

    }
}

