import java.util.Scanner;

public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
			
			int N = sc.nextInt();
			int check = sc.nextInt();
			int tall = 0;
			long cnt = 0;
			
			
			for(int i=0;i<N-1;i++) {
				tall = sc.nextInt();
				if( tall<check) {
					cnt=cnt+(check-tall);
				}else {
					check=tall;
				}
			}
			
						
			System.out.println(cnt);
	}	
} 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 check = sc.nextInt();
			int tall = 0;
			long cnt = 0;
			
			
			for(int i=0;i<N-1;i++) {
				tall = sc.nextInt();
				if( tall<check) {
					cnt=cnt+(check-tall);
				}else {
					check=tall;
				}
			}
			
						
			System.out.println(cnt);
	}	
} Main public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
			
			int N = sc.nextInt();
			int check = sc.nextInt();
			int tall = 0;
			long cnt = 0;
			
			
			for(int i=0;i<N-1;i++) {
				tall = sc.nextInt();
				if( tall<check) {
					cnt=cnt+(check-tall);
				}else {
					check=tall;
				}
			}
			
						
			System.out.println(cnt);
	} main {
		Scanner sc = new Scanner(System.in);
			
			int N = sc.nextInt();
			int check = sc.nextInt();
			int tall = 0;
			long cnt = 0;
			
			
			for(int i=0;i<N-1;i++) {
				tall = sc.nextInt();
				if( tall<check) {
					cnt=cnt+(check-tall);
				}else {
					check=tall;
				}
			}
			
						
			System.out.println(cnt);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = sc.nextInt(); N sc.nextInt() sc.nextInt sc int check = sc.nextInt(); check sc.nextInt() sc.nextInt sc int tall = 0; tall 0 long cnt = 0; cnt 0 for(int i=0;i<N-1;i++) {
				tall = sc.nextInt();
				if( tall<check) {
					cnt=cnt+(check-tall);
				}else {
					check=tall;
				}
			} int i=0; int i=0; i 0 i<N-1 i N-1 N 1 i++ i++ i {
				tall = sc.nextInt();
				if( tall<check) {
					cnt=cnt+(check-tall);
				}else {
					check=tall;
				}
			} {
				tall = sc.nextInt();
				if( tall<check) {
					cnt=cnt+(check-tall);
				}else {
					check=tall;
				}
			} tall = sc.nextInt() tall sc.nextInt() sc.nextInt sc if( tall<check) {
					cnt=cnt+(check-tall);
				}else {
					check=tall;
				} tall<check tall check {
					cnt=cnt+(check-tall);
				} cnt=cnt+(check-tall) cnt cnt+(check-tall) cnt (check-tall) check tall {
					check=tall;
				} check=tall check tall System.out.println(cnt) System.out.println System.out System System.out cnt String[] args args public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
			
			int N = sc.nextInt();
			int check = sc.nextInt();
			int tall = 0;
			long cnt = 0;
			
			
			for(int i=0;i<N-1;i++) {
				tall = sc.nextInt();
				if( tall<check) {
					cnt=cnt+(check-tall);
				}else {
					check=tall;
				}
			}
			
						
			System.out.println(cnt);
	}	
} public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
			
			int N = sc.nextInt();
			int check = sc.nextInt();
			int tall = 0;
			long cnt = 0;
			
			
			for(int i=0;i<N-1;i++) {
				tall = sc.nextInt();
				if( tall<check) {
					cnt=cnt+(check-tall);
				}else {
					check=tall;
				}
			}
			
						
			System.out.println(cnt);
	}	
} 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 check = sc.nextInt();
			int tall = 0;
			long cnt = 0;
			
			
			for(int i=0;i<N-1;i++) {
				tall = sc.nextInt();
				if( tall<check) {
					cnt=cnt+(check-tall);
				}else {
					check=tall;
				}
			}
			
						
			System.out.println(cnt);
	}	
}