import java.util.*;

public class Main{
	public static void main(String arg[]){
		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 t=a[0];
		long sum=0;
		for(int i=1;i<n;i++){
			if(t>a[i])
				sum=sum+(t-a[i]);
			else {
				t=a[i];
				continue;
			}
		}
		System.out.println(sum);
	}
} import java.util.*; util.* java public class Main{
	public static void main(String arg[]){
		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 t=a[0];
		long sum=0;
		for(int i=1;i<n;i++){
			if(t>a[i])
				sum=sum+(t-a[i]);
			else {
				t=a[i];
				continue;
			}
		}
		System.out.println(sum);
	}
} Main public static void main(String arg[]){
		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 t=a[0];
		long sum=0;
		for(int i=1;i<n;i++){
			if(t>a[i])
				sum=sum+(t-a[i]);
			else {
				t=a[i];
				continue;
			}
		}
		System.out.println(sum);
	} 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 t=a[0];
		long sum=0;
		for(int i=1;i<n;i++){
			if(t>a[i])
				sum=sum+(t-a[i]);
			else {
				t=a[i];
				continue;
			}
		}
		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 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 t=a[0]; t a[0] a 0 long sum=0; sum 0 for(int i=1;i<n;i++){
			if(t>a[i])
				sum=sum+(t-a[i]);
			else {
				t=a[i];
				continue;
			}
		} int i=1; int i=1; i 1 i<n i n i++ i++ i {
			if(t>a[i])
				sum=sum+(t-a[i]);
			else {
				t=a[i];
				continue;
			}
		} {
			if(t>a[i])
				sum=sum+(t-a[i]);
			else {
				t=a[i];
				continue;
			}
		} if(t>a[i])
				sum=sum+(t-a[i]);
			else {
				t=a[i];
				continue;
			} t>a[i] t a[i] a i sum=sum+(t-a[i]) sum sum+(t-a[i]) sum (t-a[i]) t a[i] a i {
				t=a[i];
				continue;
			} t=a[i] t a[i] a i continue; System.out.println(sum) System.out.println System.out System System.out sum String arg[] arg public class Main{
	public static void main(String arg[]){
		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 t=a[0];
		long sum=0;
		for(int i=1;i<n;i++){
			if(t>a[i])
				sum=sum+(t-a[i]);
			else {
				t=a[i];
				continue;
			}
		}
		System.out.println(sum);
	}
} public class Main{
	public static void main(String arg[]){
		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 t=a[0];
		long sum=0;
		for(int i=1;i<n;i++){
			if(t>a[i])
				sum=sum+(t-a[i]);
			else {
				t=a[i];
				continue;
			}
		}
		System.out.println(sum);
	}
} Main
import java.util.*;

public class Main{
	public static void main(String arg[]){
		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 t=a[0];
		long sum=0;
		for(int i=1;i<n;i++){
			if(t>a[i])
				sum=sum+(t-a[i]);
			else {
				t=a[i];
				continue;
			}
		}
		System.out.println(sum);
	}
}