import java.util.Scanner;

public class Main {

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

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		long ans = 0;
		int san = sc.nextInt();
		for(int i=0;i<n-1;i++) {
			int a = sc.nextInt();
			if(san>=a) {
				ans += san-a;
			}
			else {
				san = a;
			}
		}
		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();
		long ans = 0;
		int san = sc.nextInt();
		for(int i=0;i<n-1;i++) {
			int a = sc.nextInt();
			if(san>=a) {
				ans += san-a;
			}
			else {
				san = a;
			}
		}
		System.out.println(ans);
	}
}
