import 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();
        }

        int bigTall = a[0];

        long count = 0;
        for(int i = 1; i<n; i++){
            if(bigTall > a[i]){
                int sub = bigTall - a[i];
                count += sub;
            }
            else{
                bigTall = a[i];
            }
        }
        System.out.println(count);
    }
} import java.util.*; util.* java 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();
        }

        int bigTall = a[0];

        long count = 0;
        for(int i = 1; i<n; i++){
            if(bigTall > a[i]){
                int sub = bigTall - a[i];
                count += sub;
            }
            else{
                bigTall = a[i];
            }
        }
        System.out.println(count);
    }
} 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();
        }

        int bigTall = a[0];

        long count = 0;
        for(int i = 1; i<n; i++){
            if(bigTall > a[i]){
                int sub = bigTall - a[i];
                count += sub;
            }
            else{
                bigTall = a[i];
            }
        }
        System.out.println(count);
    } 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();
        }

        int bigTall = a[0];

        long count = 0;
        for(int i = 1; i<n; i++){
            if(bigTall > a[i]){
                int sub = bigTall - a[i];
                count += sub;
            }
            else{
                bigTall = a[i];
            }
        }
        System.out.println(count);
    } 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] = sc.nextInt() a[i] a i sc.nextInt() sc.nextInt sc int bigTall = a[0]; bigTall a[0] a 0 long count = 0; count 0 for(int i = 1; i<n; i++){
            if(bigTall > a[i]){
                int sub = bigTall - a[i];
                count += sub;
            }
            else{
                bigTall = a[i];
            }
        } int i = 1; int i = 1; i 1 i<n i n i++ i++ i {
            if(bigTall > a[i]){
                int sub = bigTall - a[i];
                count += sub;
            }
            else{
                bigTall = a[i];
            }
        } {
            if(bigTall > a[i]){
                int sub = bigTall - a[i];
                count += sub;
            }
            else{
                bigTall = a[i];
            }
        } if(bigTall > a[i]){
                int sub = bigTall - a[i];
                count += sub;
            }
            else{
                bigTall = a[i];
            } bigTall > a[i] bigTall a[i] a i {
                int sub = bigTall - a[i];
                count += sub;
            } int sub = bigTall - a[i]; sub bigTall - a[i] bigTall a[i] a i count += sub count sub {
                bigTall = a[i];
            } bigTall = a[i] bigTall a[i] a i System.out.println(count) System.out.println System.out System System.out count 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();
        }

        int bigTall = a[0];

        long count = 0;
        for(int i = 1; i<n; i++){
            if(bigTall > a[i]){
                int sub = bigTall - a[i];
                count += sub;
            }
            else{
                bigTall = a[i];
            }
        }
        System.out.println(count);
    }
} 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();
        }

        int bigTall = a[0];

        long count = 0;
        for(int i = 1; i<n; i++){
            if(bigTall > a[i]){
                int sub = bigTall - a[i];
                count += sub;
            }
            else{
                bigTall = a[i];
            }
        }
        System.out.println(count);
    }
} Main
import 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();
        }

        int bigTall = a[0];

        long count = 0;
        for(int i = 1; i<n; i++){
            if(bigTall > a[i]){
                int sub = bigTall - a[i];
                count += sub;
            }
            else{
                bigTall = a[i];
            }
        }
        System.out.println(count);
    }
}