import java.util.Scanner;

public class Main {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long sum = 0;
        int tmp = 0;
        int next = 0;

        // 一人目
        next = sc.nextInt();
        tmp = next;

        for (int i = 1; i < n; i++) {
            next = sc.nextInt();
            int diff = 0;
            if (next < tmp) {
                diff = tmp - next;
                sum += diff;
            }
            tmp = next + diff;
        }
        System.out.println(sum);
    }
} import java.util.Scanner; Scanner java.util public class Main {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long sum = 0;
        int tmp = 0;
        int next = 0;

        // 一人目
        next = sc.nextInt();
        tmp = next;

        for (int i = 1; i < n; i++) {
            next = sc.nextInt();
            int diff = 0;
            if (next < tmp) {
                diff = tmp - next;
                sum += diff;
            }
            tmp = next + diff;
        }
        System.out.println(sum);
    }
} Main public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long sum = 0;
        int tmp = 0;
        int next = 0;

        // 一人目
        next = sc.nextInt();
        tmp = next;

        for (int i = 1; i < n; i++) {
            next = sc.nextInt();
            int diff = 0;
            if (next < tmp) {
                diff = tmp - next;
                sum += diff;
            }
            tmp = next + diff;
        }
        System.out.println(sum);
    } main {

        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long sum = 0;
        int tmp = 0;
        int next = 0;

        // 一人目
        next = sc.nextInt();
        tmp = next;

        for (int i = 1; i < n; i++) {
            next = sc.nextInt();
            int diff = 0;
            if (next < tmp) {
                diff = tmp - next;
                sum += diff;
            }
            tmp = next + diff;
        }
        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 sum = 0; sum 0 int tmp = 0; tmp 0 int next = 0; next 0 next = sc.nextInt() next sc.nextInt() sc.nextInt sc tmp = next tmp next for (int i = 1; i < n; i++) {
            next = sc.nextInt();
            int diff = 0;
            if (next < tmp) {
                diff = tmp - next;
                sum += diff;
            }
            tmp = next + diff;
        } int i = 1; int i = 1; i 1 i < n i n i++ i++ i {
            next = sc.nextInt();
            int diff = 0;
            if (next < tmp) {
                diff = tmp - next;
                sum += diff;
            }
            tmp = next + diff;
        } {
            next = sc.nextInt();
            int diff = 0;
            if (next < tmp) {
                diff = tmp - next;
                sum += diff;
            }
            tmp = next + diff;
        } next = sc.nextInt() next sc.nextInt() sc.nextInt sc int diff = 0; diff 0 if (next < tmp) {
                diff = tmp - next;
                sum += diff;
            } next < tmp next tmp {
                diff = tmp - next;
                sum += diff;
            } diff = tmp - next diff tmp - next tmp next sum += diff sum diff tmp = next + diff tmp next + diff next diff 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) {

        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long sum = 0;
        int tmp = 0;
        int next = 0;

        // 一人目
        next = sc.nextInt();
        tmp = next;

        for (int i = 1; i < n; i++) {
            next = sc.nextInt();
            int diff = 0;
            if (next < tmp) {
                diff = tmp - next;
                sum += diff;
            }
            tmp = next + diff;
        }
        System.out.println(sum);
    }
} public class Main {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long sum = 0;
        int tmp = 0;
        int next = 0;

        // 一人目
        next = sc.nextInt();
        tmp = next;

        for (int i = 1; i < n; i++) {
            next = sc.nextInt();
            int diff = 0;
            if (next < tmp) {
                diff = tmp - next;
                sum += diff;
            }
            tmp = next + diff;
        }
        System.out.println(sum);
    }
} Main
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long sum = 0;
        int tmp = 0;
        int next = 0;

        // 一人目
        next = sc.nextInt();
        tmp = next;

        for (int i = 1; i < n; i++) {
            next = sc.nextInt();
            int diff = 0;
            if (next < tmp) {
                diff = tmp - next;
                sum += diff;
            }
            tmp = next + diff;
        }
        System.out.println(sum);
    }
}