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);
        CStep solver = new CStep();
        solver.solve(1, in, out);
        out.close();
    }

    static class CStep {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int n = Integer.parseInt(in.next());
            long[] a = new long[n];
            for (int i = 0; i < n; i++) {
                a[i] = Long.parseLong(in.next());
            }
            long ans = 0;
            for (int i = 1; i < n; i++) {
                if (a[i - 1] - a[i] > 0) {
                    ans += a[i - 1] - a[i];
                    a[i] += a[i - 1] - a[i];
                }
            }

            // 出力
            out.println(ans);

        }

    }
}
 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);
        CStep solver = new CStep();
        solver.solve(1, in, out);
        out.close();
    }

    static class CStep {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int n = Integer.parseInt(in.next());
            long[] a = new long[n];
            for (int i = 0; i < n; i++) {
                a[i] = Long.parseLong(in.next());
            }
            long ans = 0;
            for (int i = 1; i < n; i++) {
                if (a[i - 1] - a[i] > 0) {
                    ans += a[i - 1] - a[i];
                    a[i] += a[i - 1] - a[i];
                }
            }

            // 出力
            out.println(ans);

        }

    }
} 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);
        CStep solver = new CStep();
        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);
        CStep solver = new CStep();
        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) CStep solver = new CStep(); solver new CStep() solver.solve(1, in, out) solver.solve solver 1 in out out.close() out.close out String[] args args static class CStep {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int n = Integer.parseInt(in.next());
            long[] a = new long[n];
            for (int i = 0; i < n; i++) {
                a[i] = Long.parseLong(in.next());
            }
            long ans = 0;
            for (int i = 1; i < n; i++) {
                if (a[i - 1] - a[i] > 0) {
                    ans += a[i - 1] - a[i];
                    a[i] += a[i - 1] - a[i];
                }
            }

            // 出力
            out.println(ans);

        }

    } CStep public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int n = Integer.parseInt(in.next());
            long[] a = new long[n];
            for (int i = 0; i < n; i++) {
                a[i] = Long.parseLong(in.next());
            }
            long ans = 0;
            for (int i = 1; i < n; i++) {
                if (a[i - 1] - a[i] > 0) {
                    ans += a[i - 1] - a[i];
                    a[i] += a[i - 1] - a[i];
                }
            }

            // 出力
            out.println(ans);

        } solve {
            // 入力
            int n = Integer.parseInt(in.next());
            long[] a = new long[n];
            for (int i = 0; i < n; i++) {
                a[i] = Long.parseLong(in.next());
            }
            long ans = 0;
            for (int i = 1; i < n; i++) {
                if (a[i - 1] - a[i] > 0) {
                    ans += a[i - 1] - a[i];
                    a[i] += a[i - 1] - a[i];
                }
            }

            // 出力
            out.println(ans);

        } int n = Integer.parseInt(in.next()); n Integer.parseInt(in.next()) Integer.parseInt Integer in.next() in.next in long[] a = new long[n]; a new long[n] n for (int i = 0; i < n; i++) {
                a[i] = Long.parseLong(in.next());
            } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
                a[i] = Long.parseLong(in.next());
            } {
                a[i] = Long.parseLong(in.next());
            } a[i] = Long.parseLong(in.next()) a[i] a i Long.parseLong(in.next()) Long.parseLong Long in.next() in.next in long ans = 0; ans 0 for (int i = 1; i < n; i++) {
                if (a[i - 1] - a[i] > 0) {
                    ans += a[i - 1] - a[i];
                    a[i] += a[i - 1] - a[i];
                }
            } int i = 1; int i = 1; i 1 i < n i n i++ i++ i {
                if (a[i - 1] - a[i] > 0) {
                    ans += a[i - 1] - a[i];
                    a[i] += a[i - 1] - a[i];
                }
            } {
                if (a[i - 1] - a[i] > 0) {
                    ans += a[i - 1] - a[i];
                    a[i] += a[i - 1] - a[i];
                }
            } if (a[i - 1] - a[i] > 0) {
                    ans += a[i - 1] - a[i];
                    a[i] += a[i - 1] - a[i];
                } a[i - 1] - a[i] > 0 a[i - 1] - a[i] a[i - 1] a i - 1 i 1 a[i] a i 0 {
                    ans += a[i - 1] - a[i];
                    a[i] += a[i - 1] - a[i];
                } ans += a[i - 1] - a[i] ans a[i - 1] - a[i] a[i - 1] a i - 1 i 1 a[i] a i a[i] += a[i - 1] - a[i] a[i] a i a[i - 1] - a[i] a[i - 1] a i - 1 i 1 a[i] a i out.println(ans) out.println out ans int testNumber testNumber Scanner in in PrintWriter out out 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);
        CStep solver = new CStep();
        solver.solve(1, in, out);
        out.close();
    }

    static class CStep {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int n = Integer.parseInt(in.next());
            long[] a = new long[n];
            for (int i = 0; i < n; i++) {
                a[i] = Long.parseLong(in.next());
            }
            long ans = 0;
            for (int i = 1; i < n; i++) {
                if (a[i - 1] - a[i] > 0) {
                    ans += a[i - 1] - a[i];
                    a[i] += a[i - 1] - a[i];
                }
            }

            // 出力
            out.println(ans);

        }

    }
} 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);
        CStep solver = new CStep();
        solver.solve(1, in, out);
        out.close();
    }

    static class CStep {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int n = Integer.parseInt(in.next());
            long[] a = new long[n];
            for (int i = 0; i < n; i++) {
                a[i] = Long.parseLong(in.next());
            }
            long ans = 0;
            for (int i = 1; i < n; i++) {
                if (a[i - 1] - a[i] > 0) {
                    ans += a[i - 1] - a[i];
                    a[i] += a[i - 1] - a[i];
                }
            }

            // 出力
            out.println(ans);

        }

    }
} 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);
        CStep solver = new CStep();
        solver.solve(1, in, out);
        out.close();
    }

    static class CStep {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            // 入力
            int n = Integer.parseInt(in.next());
            long[] a = new long[n];
            for (int i = 0; i < n; i++) {
                a[i] = Long.parseLong(in.next());
            }
            long ans = 0;
            for (int i = 1; i < n; i++) {
                if (a[i - 1] - a[i] > 0) {
                    ans += a[i - 1] - a[i];
                    a[i] += a[i - 1] - a[i];
                }
            }

            // 出力
            out.println(ans);

        }

    }
}

