import java.util.Scanner;

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

        long result = 0;
        int max = a[0];
        for(int i = 0; i < n; i++) {
            if (max <= a[i]) max = a[i];
            result += max - a[i];
        }
        System.out.println(result);
    }
} 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();
        int[] a = new int[n];
        for (int i = 0; i < n; i++) a[i] = sc.nextInt();

        long result = 0;
        int max = a[0];
        for(int i = 0; i < n; i++) {
            if (max <= a[i]) max = a[i];
            result += max - a[i];
        }
        System.out.println(result);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n];
        for (int i = 0; i < n; i++) a[i] = sc.nextInt();

        long result = 0;
        int max = a[0];
        for(int i = 0; i < n; i++) {
            if (max <= a[i]) max = a[i];
            result += max - a[i];
        }
        System.out.println(result);
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n];
        for (int i = 0; i < n; i++) a[i] = sc.nextInt();

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

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

        long result = 0;
        int max = a[0];
        for(int i = 0; i < n; i++) {
            if (max <= a[i]) max = a[i];
            result += max - a[i];
        }
        System.out.println(result);
    }
} Main
import java.util.Scanner;

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

        long result = 0;
        int max = a[0];
        for(int i = 0; i < n; i++) {
            if (max <= a[i]) max = a[i];
            result += max - a[i];
        }
        System.out.println(result);
    }
}
