import java.util.Scanner;

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

    }
   
} Main public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        // 配列
        int[] a = new int[n];
        a[0] = sc.nextInt();
        int mx = a[0];
        long sum = 0;
        for(int i=1;i<n;i++){
            a[i] = sc.nextInt();
            if(a[i] < mx) {
                sum += (mx - a[i]);
            } else {
                mx = a[i];
            }
        }
            System.out.println(sum);

    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        // 配列
        int[] a = new int[n];
        a[0] = sc.nextInt();
        int mx = a[0];
        long sum = 0;
        for(int i=1;i<n;i++){
            a[i] = sc.nextInt();
            if(a[i] < mx) {
                sum += (mx - a[i]);
            } else {
                mx = a[i];
            }
        }
            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 int[] a = new int[n]; a new int[n] n a[0] = sc.nextInt() a[0] a 0 sc.nextInt() sc.nextInt sc int mx = a[0]; mx a[0] a 0 long sum = 0; sum 0 for(int i=1;i<n;i++){
            a[i] = sc.nextInt();
            if(a[i] < mx) {
                sum += (mx - a[i]);
            } else {
                mx = a[i];
            }
        } int i=1; int i=1; i 1 i<n i n i++ i++ i {
            a[i] = sc.nextInt();
            if(a[i] < mx) {
                sum += (mx - a[i]);
            } else {
                mx = a[i];
            }
        } {
            a[i] = sc.nextInt();
            if(a[i] < mx) {
                sum += (mx - a[i]);
            } else {
                mx = a[i];
            }
        } a[i] = sc.nextInt() a[i] a i sc.nextInt() sc.nextInt sc if(a[i] < mx) {
                sum += (mx - a[i]);
            } else {
                mx = a[i];
            } a[i] < mx a[i] a i mx {
                sum += (mx - a[i]);
            } sum += (mx - a[i]) sum (mx - a[i]) mx a[i] a i {
                mx = a[i];
            } mx = a[i] mx a[i] a i 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();
        // 配列
        int[] a = new int[n];
        a[0] = sc.nextInt();
        int mx = a[0];
        long sum = 0;
        for(int i=1;i<n;i++){
            a[i] = sc.nextInt();
            if(a[i] < mx) {
                sum += (mx - a[i]);
            } else {
                mx = a[i];
            }
        }
            System.out.println(sum);

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

    }
   
}

