import java.util.*;

public class Main {
	public static void main(String[] args) {
		Scanner scn  = new Scanner(System.in);
		int n = scn.nextInt();
		int[] arr = new int[n];
		for(int i=0;i<n;i++)
			arr[i] = scn.nextInt();
		long ans = 0;
		for(int i=1;i<n;i++)
		{
			if(arr[i]<arr[i-1])
				{
					ans += (arr[i-1]-arr[i]);
					arr[i] = arr[i-1];
				}
		}
		System.out.println(ans);
		
	}
} import java.util.*; util.* java public class Main {
	public static void main(String[] args) {
		Scanner scn  = new Scanner(System.in);
		int n = scn.nextInt();
		int[] arr = new int[n];
		for(int i=0;i<n;i++)
			arr[i] = scn.nextInt();
		long ans = 0;
		for(int i=1;i<n;i++)
		{
			if(arr[i]<arr[i-1])
				{
					ans += (arr[i-1]-arr[i]);
					arr[i] = arr[i-1];
				}
		}
		System.out.println(ans);
		
	}
} Main public static void main(String[] args) {
		Scanner scn  = new Scanner(System.in);
		int n = scn.nextInt();
		int[] arr = new int[n];
		for(int i=0;i<n;i++)
			arr[i] = scn.nextInt();
		long ans = 0;
		for(int i=1;i<n;i++)
		{
			if(arr[i]<arr[i-1])
				{
					ans += (arr[i-1]-arr[i]);
					arr[i] = arr[i-1];
				}
		}
		System.out.println(ans);
		
	} main {
		Scanner scn  = new Scanner(System.in);
		int n = scn.nextInt();
		int[] arr = new int[n];
		for(int i=0;i<n;i++)
			arr[i] = scn.nextInt();
		long ans = 0;
		for(int i=1;i<n;i++)
		{
			if(arr[i]<arr[i-1])
				{
					ans += (arr[i-1]-arr[i]);
					arr[i] = arr[i-1];
				}
		}
		System.out.println(ans);
		
	} Scanner scn  = new Scanner(System.in); scn new Scanner(System.in) int n = scn.nextInt(); n scn.nextInt() scn.nextInt scn int[] arr = new int[n]; arr new int[n] n for(int i=0;i<n;i++)
			arr[i] = scn.nextInt(); int i=0; int i=0; i 0 i<n i n i++ i++ i arr[i] = scn.nextInt(); arr[i] = scn.nextInt() arr[i] arr i scn.nextInt() scn.nextInt scn long ans = 0; ans 0 for(int i=1;i<n;i++)
		{
			if(arr[i]<arr[i-1])
				{
					ans += (arr[i-1]-arr[i]);
					arr[i] = arr[i-1];
				}
		} int i=1; int i=1; i 1 i<n i n i++ i++ i {
			if(arr[i]<arr[i-1])
				{
					ans += (arr[i-1]-arr[i]);
					arr[i] = arr[i-1];
				}
		} {
			if(arr[i]<arr[i-1])
				{
					ans += (arr[i-1]-arr[i]);
					arr[i] = arr[i-1];
				}
		} if(arr[i]<arr[i-1])
				{
					ans += (arr[i-1]-arr[i]);
					arr[i] = arr[i-1];
				} arr[i]<arr[i-1] arr[i] arr i arr[i-1] arr i-1 i 1 {
					ans += (arr[i-1]-arr[i]);
					arr[i] = arr[i-1];
				} ans += (arr[i-1]-arr[i]) ans (arr[i-1]-arr[i]) arr[i-1] arr i-1 i 1 arr[i] arr i arr[i] = arr[i-1] arr[i] arr i arr[i-1] arr i-1 i 1 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 scn  = new Scanner(System.in);
		int n = scn.nextInt();
		int[] arr = new int[n];
		for(int i=0;i<n;i++)
			arr[i] = scn.nextInt();
		long ans = 0;
		for(int i=1;i<n;i++)
		{
			if(arr[i]<arr[i-1])
				{
					ans += (arr[i-1]-arr[i]);
					arr[i] = arr[i-1];
				}
		}
		System.out.println(ans);
		
	}
} public class Main {
	public static void main(String[] args) {
		Scanner scn  = new Scanner(System.in);
		int n = scn.nextInt();
		int[] arr = new int[n];
		for(int i=0;i<n;i++)
			arr[i] = scn.nextInt();
		long ans = 0;
		for(int i=1;i<n;i++)
		{
			if(arr[i]<arr[i-1])
				{
					ans += (arr[i-1]-arr[i]);
					arr[i] = arr[i-1];
				}
		}
		System.out.println(ans);
		
	}
} Main
import java.util.*;

public class Main {
	public static void main(String[] args) {
		Scanner scn  = new Scanner(System.in);
		int n = scn.nextInt();
		int[] arr = new int[n];
		for(int i=0;i<n;i++)
			arr[i] = scn.nextInt();
		long ans = 0;
		for(int i=1;i<n;i++)
		{
			if(arr[i]<arr[i-1])
				{
					ans += (arr[i-1]-arr[i]);
					arr[i] = arr[i-1];
				}
		}
		System.out.println(ans);
		
	}
}
