import java.util.Scanner;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long a[] = new long[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextInt();
        }
        sc.close();

        long b[] = new long[n];
        b[0] = 0;
        for (int i = 1; i < n; i++) {
            if (a[i - 1] <= a[i]) {
                b[i] = 0;
            } else {
                b[i] = a[i - 1] - a[i];
            }
            a[i] += b[i];
        }

        long sum = 0;
        for (int i = 0; i < n; i++) {
            sum += b[i];
        }
        System.out.println(sum);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long a[] = new long[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextInt();
        }
        sc.close();

        long b[] = new long[n];
        b[0] = 0;
        for (int i = 1; i < n; i++) {
            if (a[i - 1] <= a[i]) {
                b[i] = 0;
            } else {
                b[i] = a[i - 1] - a[i];
            }
            a[i] += b[i];
        }

        long sum = 0;
        for (int i = 0; i < n; i++) {
            sum += b[i];
        }
        System.out.println(sum);
    }
} Main public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long a[] = new long[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextInt();
        }
        sc.close();

        long b[] = new long[n];
        b[0] = 0;
        for (int i = 1; i < n; i++) {
            if (a[i - 1] <= a[i]) {
                b[i] = 0;
            } else {
                b[i] = a[i - 1] - a[i];
            }
            a[i] += b[i];
        }

        long sum = 0;
        for (int i = 0; i < n; i++) {
            sum += b[i];
        }
        System.out.println(sum);
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long a[] = new long[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextInt();
        }
        sc.close();

        long b[] = new long[n];
        b[0] = 0;
        for (int i = 1; i < n; i++) {
            if (a[i - 1] <= a[i]) {
                b[i] = 0;
            } else {
                b[i] = a[i - 1] - a[i];
            }
            a[i] += b[i];
        }

        long sum = 0;
        for (int i = 0; i < n; i++) {
            sum += b[i];
        }
        System.out.println(sum);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc long a[] = new long[n]; a new long[n] n for (int i = 0; i < n; i++) {
            a[i] = sc.nextInt();
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            a[i] = sc.nextInt();
        } {
            a[i] = sc.nextInt();
        } a[i] = sc.nextInt() a[i] a i sc.nextInt() sc.nextInt sc sc.close() sc.close sc long b[] = new long[n]; b new long[n] n b[0] = 0 b[0] b 0 0 for (int i = 1; i < n; i++) {
            if (a[i - 1] <= a[i]) {
                b[i] = 0;
            } else {
                b[i] = a[i - 1] - a[i];
            }
            a[i] += b[i];
        } int i = 1; int i = 1; i 1 i < n i n i++ i++ i {
            if (a[i - 1] <= a[i]) {
                b[i] = 0;
            } else {
                b[i] = a[i - 1] - a[i];
            }
            a[i] += b[i];
        } {
            if (a[i - 1] <= a[i]) {
                b[i] = 0;
            } else {
                b[i] = a[i - 1] - a[i];
            }
            a[i] += b[i];
        } if (a[i - 1] <= a[i]) {
                b[i] = 0;
            } else {
                b[i] = a[i - 1] - a[i];
            } a[i - 1] <= a[i] a[i - 1] a i - 1 i 1 a[i] a i {
                b[i] = 0;
            } b[i] = 0 b[i] b i 0 {
                b[i] = a[i - 1] - a[i];
            } b[i] = a[i - 1] - a[i] b[i] b i a[i - 1] - a[i] a[i - 1] a i - 1 i 1 a[i] a i a[i] += b[i] a[i] a i b[i] b i long sum = 0; sum 0 for (int i = 0; i < n; i++) {
            sum += b[i];
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            sum += b[i];
        } {
            sum += b[i];
        } sum += b[i] sum b[i] b i System.out.println(sum) System.out.println System.out System System.out sum String[] args args public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long a[] = new long[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextInt();
        }
        sc.close();

        long b[] = new long[n];
        b[0] = 0;
        for (int i = 1; i < n; i++) {
            if (a[i - 1] <= a[i]) {
                b[i] = 0;
            } else {
                b[i] = a[i - 1] - a[i];
            }
            a[i] += b[i];
        }

        long sum = 0;
        for (int i = 0; i < n; i++) {
            sum += b[i];
        }
        System.out.println(sum);
    }
} public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long a[] = new long[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextInt();
        }
        sc.close();

        long b[] = new long[n];
        b[0] = 0;
        for (int i = 1; i < n; i++) {
            if (a[i - 1] <= a[i]) {
                b[i] = 0;
            } else {
                b[i] = a[i - 1] - a[i];
            }
            a[i] += b[i];
        }

        long sum = 0;
        for (int i = 0; i < n; i++) {
            sum += b[i];
        }
        System.out.println(sum);
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long a[] = new long[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextInt();
        }
        sc.close();

        long b[] = new long[n];
        b[0] = 0;
        for (int i = 1; i < n; i++) {
            if (a[i - 1] <= a[i]) {
                b[i] = 0;
            } else {
                b[i] = a[i - 1] - a[i];
            }
            a[i] += b[i];
        }

        long sum = 0;
        for (int i = 0; i < n; i++) {
            sum += b[i];
        }
        System.out.println(sum);
    }
}
