import java.util.Scanner;

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

        long ans = 0;
        int max = 0;
        for (int i = 0; i < n; i++) {
            max = Math.max(max, a[i]);
            ans += max - a[i];
        }
        System.out.println(ans);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = Integer.parseInt(sc.next());
        }

        long ans = 0;
        int max = 0;
        for (int i = 0; i < n; i++) {
            max = Math.max(max, a[i]);
            ans += max - a[i];
        }
        System.out.println(ans);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = Integer.parseInt(sc.next());
        }

        long ans = 0;
        int max = 0;
        for (int i = 0; i < n; i++) {
            max = Math.max(max, a[i]);
            ans += max - a[i];
        }
        System.out.println(ans);
    } main {
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = Integer.parseInt(sc.next());
        }

        long ans = 0;
        int max = 0;
        for (int i = 0; i < n; i++) {
            max = Math.max(max, a[i]);
            ans += max - a[i];
        }
        System.out.println(ans);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = Integer.parseInt(sc.next()); n Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc int[] a = new int[n]; a new int[n] n for (int i = 0; i < n; i++) {
            a[i] = Integer.parseInt(sc.next());
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            a[i] = Integer.parseInt(sc.next());
        } {
            a[i] = Integer.parseInt(sc.next());
        } a[i] = Integer.parseInt(sc.next()) a[i] a i Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc long ans = 0; ans 0 int max = 0; max 0 for (int i = 0; i < n; i++) {
            max = Math.max(max, a[i]);
            ans += max - a[i];
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            max = Math.max(max, a[i]);
            ans += max - a[i];
        } {
            max = Math.max(max, a[i]);
            ans += max - a[i];
        } max = Math.max(max, a[i]) max Math.max(max, a[i]) Math.max Math max a[i] a i ans += max - a[i] ans max - a[i] max a[i] a i System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = Integer.parseInt(sc.next());
        }

        long ans = 0;
        int max = 0;
        for (int i = 0; i < n; i++) {
            max = Math.max(max, a[i]);
            ans += max - a[i];
        }
        System.out.println(ans);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = Integer.parseInt(sc.next());
        }

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

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

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