import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        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.nextLong();
        }
        long sum = 0;
        for (int i = 1; i < n; i++) {
            if (a[i] < a[i - 1]) {
                sum += (a[i - 1] - a[i]);
                a[i] = a[i - 1];
            }
        }
        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[] a = new long[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextLong();
        }
        long sum = 0;
        for (int i = 1; i < n; i++) {
            if (a[i] < a[i - 1]) {
                sum += (a[i - 1] - a[i]);
                a[i] = a[i - 1];
            }
        }
        System.out.println(sum);
    }
} Main public static void main(String[] args) {
        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.nextLong();
        }
        long sum = 0;
        for (int i = 1; i < n; i++) {
            if (a[i] < a[i - 1]) {
                sum += (a[i - 1] - a[i]);
                a[i] = a[i - 1];
            }
        }
        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.nextLong();
        }
        long sum = 0;
        for (int i = 1; i < n; i++) {
            if (a[i] < a[i - 1]) {
                sum += (a[i - 1] - a[i]);
                a[i] = a[i - 1];
            }
        }
        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.nextLong();
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            a[i] = sc.nextLong();
        } {
            a[i] = sc.nextLong();
        } a[i] = sc.nextLong() a[i] a i sc.nextLong() sc.nextLong sc long sum = 0; sum 0 for (int i = 1; i < n; i++) {
            if (a[i] < a[i - 1]) {
                sum += (a[i - 1] - a[i]);
                a[i] = a[i - 1];
            }
        } int i = 1; int i = 1; i 1 i < n i n i++ i++ i {
            if (a[i] < a[i - 1]) {
                sum += (a[i - 1] - a[i]);
                a[i] = a[i - 1];
            }
        } {
            if (a[i] < a[i - 1]) {
                sum += (a[i - 1] - a[i]);
                a[i] = a[i - 1];
            }
        } if (a[i] < a[i - 1]) {
                sum += (a[i - 1] - a[i]);
                a[i] = a[i - 1];
            } a[i] < a[i - 1] a[i] a i a[i - 1] a i - 1 i 1 {
                sum += (a[i - 1] - a[i]);
                a[i] = a[i - 1];
            } sum += (a[i - 1] - a[i]) sum (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 - 1] a i - 1 i 1 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[] a = new long[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextLong();
        }
        long sum = 0;
        for (int i = 1; i < n; i++) {
            if (a[i] < a[i - 1]) {
                sum += (a[i - 1] - a[i]);
                a[i] = a[i - 1];
            }
        }
        System.out.println(sum);
    }
} public class Main {

    public static void main(String[] args) {
        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.nextLong();
        }
        long sum = 0;
        for (int i = 1; i < n; i++) {
            if (a[i] < a[i - 1]) {
                sum += (a[i - 1] - a[i]);
                a[i] = a[i - 1];
            }
        }
        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[] a = new long[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextLong();
        }
        long sum = 0;
        for (int i = 1; i < n; i++) {
            if (a[i] < a[i - 1]) {
                sum += (a[i - 1] - a[i]);
                a[i] = a[i - 1];
            }
        }
        System.out.println(sum);
    }
}
