import java.util.Scanner;

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 < a.length; i++) {
			a[i]=sc.nextInt();
		}
		long ans=0;
		for (int i = 0; i < a.length-1; i++) {
			if(a[i]>=a[i+1]){ans=ans+(a[i]-a[i+1]);a[i+1]=a[i];}
		}
		System.out.println(""+ans);
	}
} 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();
		int[] a=new int[n];
		for (int i = 0; i < a.length; i++) {
			a[i]=sc.nextInt();
		}
		long ans=0;
		for (int i = 0; i < a.length-1; i++) {
			if(a[i]>=a[i+1]){ans=ans+(a[i]-a[i+1]);a[i+1]=a[i];}
		}
		System.out.println(""+ans);
	}
} 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 < a.length; i++) {
			a[i]=sc.nextInt();
		}
		long ans=0;
		for (int i = 0; i < a.length-1; i++) {
			if(a[i]>=a[i+1]){ans=ans+(a[i]-a[i+1]);a[i+1]=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 < a.length; i++) {
			a[i]=sc.nextInt();
		}
		long ans=0;
		for (int i = 0; i < a.length-1; i++) {
			if(a[i]>=a[i+1]){ans=ans+(a[i]-a[i+1]);a[i+1]=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 < a.length; i++) {
			a[i]=sc.nextInt();
		} int i = 0; int i = 0; i 0 i < a.length i a.length a a.length i++ i++ i {
			a[i]=sc.nextInt();
		} {
			a[i]=sc.nextInt();
		} a[i]=sc.nextInt() a[i] a i sc.nextInt() sc.nextInt sc long ans=0; ans 0 for (int i = 0; i < a.length-1; i++) {
			if(a[i]>=a[i+1]){ans=ans+(a[i]-a[i+1]);a[i+1]=a[i];}
		} int i = 0; int i = 0; i 0 i < a.length-1 i a.length-1 a.length a a.length 1 i++ i++ i {
			if(a[i]>=a[i+1]){ans=ans+(a[i]-a[i+1]);a[i+1]=a[i];}
		} {
			if(a[i]>=a[i+1]){ans=ans+(a[i]-a[i+1]);a[i+1]=a[i];}
		} if(a[i]>=a[i+1]){ans=ans+(a[i]-a[i+1]);a[i+1]=a[i];} a[i]>=a[i+1] a[i] a i a[i+1] a i+1 i 1 {ans=ans+(a[i]-a[i+1]);a[i+1]=a[i];} ans=ans+(a[i]-a[i+1]) ans ans+(a[i]-a[i+1]) ans (a[i]-a[i+1]) a[i] a i a[i+1] a i+1 i 1 a[i+1]=a[i] a[i+1] a i+1 i 1 a[i] a i System.out.println(""+ans) System.out.println System.out System System.out ""+ans "" ans 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 < a.length; i++) {
			a[i]=sc.nextInt();
		}
		long ans=0;
		for (int i = 0; i < a.length-1; i++) {
			if(a[i]>=a[i+1]){ans=ans+(a[i]-a[i+1]);a[i+1]=a[i];}
		}
		System.out.println(""+ans);
	}
} 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 < a.length; i++) {
			a[i]=sc.nextInt();
		}
		long ans=0;
		for (int i = 0; i < a.length-1; i++) {
			if(a[i]>=a[i+1]){ans=ans+(a[i]-a[i+1]);a[i+1]=a[i];}
		}
		System.out.println(""+ans);
	}
} Main
import java.util.Scanner;

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 < a.length; i++) {
			a[i]=sc.nextInt();
		}
		long ans=0;
		for (int i = 0; i < a.length-1; i++) {
			if(a[i]>=a[i+1]){ans=ans+(a[i]-a[i+1]);a[i+1]=a[i];}
		}
		System.out.println(""+ans);
	}
}