import java.math.BigDecimal;
import java.util.Scanner;
class Main {
    public static void main(final 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 max=a[0];
        BigDecimal ans =new BigDecimal(0);
        for(int i=1;i<N;i++){
            if(max>a[i]){
                ans = ans.add(BigDecimal.valueOf(max - a[i]));
            }else{
                max = a[i];
            }
        }
        System.out.println(ans);
    }
} import java.math.BigDecimal; BigDecimal java.math import java.util.Scanner; Scanner java.util class Main {
    public static void main(final 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 max=a[0];
        BigDecimal ans =new BigDecimal(0);
        for(int i=1;i<N;i++){
            if(max>a[i]){
                ans = ans.add(BigDecimal.valueOf(max - a[i]));
            }else{
                max = a[i];
            }
        }
        System.out.println(ans);
    }
} Main public static void main(final 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 max=a[0];
        BigDecimal ans =new BigDecimal(0);
        for(int i=1;i<N;i++){
            if(max>a[i]){
                ans = ans.add(BigDecimal.valueOf(max - a[i]));
            }else{
                max = a[i];
            }
        }
        System.out.println(ans);
    } 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 max=a[0];
        BigDecimal ans =new BigDecimal(0);
        for(int i=1;i<N;i++){
            if(max>a[i]){
                ans = ans.add(BigDecimal.valueOf(max - a[i]));
            }else{
                max = a[i];
            }
        }
        System.out.println(ans);
    } 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 int max=a[0]; max a[0] a 0 BigDecimal ans =new BigDecimal(0); ans new BigDecimal(0) for(int i=1;i<N;i++){
            if(max>a[i]){
                ans = ans.add(BigDecimal.valueOf(max - a[i]));
            }else{
                max = a[i];
            }
        } int i=1; int i=1; i 1 i<N i N i++ i++ i {
            if(max>a[i]){
                ans = ans.add(BigDecimal.valueOf(max - a[i]));
            }else{
                max = a[i];
            }
        } {
            if(max>a[i]){
                ans = ans.add(BigDecimal.valueOf(max - a[i]));
            }else{
                max = a[i];
            }
        } if(max>a[i]){
                ans = ans.add(BigDecimal.valueOf(max - a[i]));
            }else{
                max = a[i];
            } max>a[i] max a[i] a i {
                ans = ans.add(BigDecimal.valueOf(max - a[i]));
            } ans = ans.add(BigDecimal.valueOf(max - a[i])) ans ans.add(BigDecimal.valueOf(max - a[i])) ans.add ans BigDecimal.valueOf(max - a[i]) BigDecimal.valueOf BigDecimal max - a[i] max a[i] a i {
                max = a[i];
            } max = a[i] max a[i] a i System.out.println(ans) System.out.println System.out System System.out ans final String[] args args
import java.math.BigDecimal;
import java.util.Scanner;
class Main {
    public static void main(final 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 max=a[0];
        BigDecimal ans =new BigDecimal(0);
        for(int i=1;i<N;i++){
            if(max>a[i]){
                ans = ans.add(BigDecimal.valueOf(max - a[i]));
            }else{
                max = a[i];
            }
        }
        System.out.println(ans);
    }
}