
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];
		long count = 0L;

		for (int i = 0; i < n; i++) {
			a[i] = sc.nextInt();
		}

		for (int i = 0; i < n - 1; i++) {
			if (a[i] > a[i + 1]) {
				count += (a[i] - a[i + 1]);
				a[i + 1] = a[i];
			}
		}

		System.out.println(count);

	}
} 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];
		long count = 0L;

		for (int i = 0; i < n; i++) {
			a[i] = sc.nextInt();
		}

		for (int i = 0; i < n - 1; i++) {
			if (a[i] > a[i + 1]) {
				count += (a[i] - a[i + 1]);
				a[i + 1] = a[i];
			}
		}

		System.out.println(count);

	}
} Main public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		int[] a = new int[n];
		long count = 0L;

		for (int i = 0; i < n; i++) {
			a[i] = sc.nextInt();
		}

		for (int i = 0; i < n - 1; i++) {
			if (a[i] > a[i + 1]) {
				count += (a[i] - a[i + 1]);
				a[i + 1] = a[i];
			}
		}

		System.out.println(count);

	} main {

		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		int[] a = new int[n];
		long count = 0L;

		for (int i = 0; i < n; i++) {
			a[i] = sc.nextInt();
		}

		for (int i = 0; i < n - 1; i++) {
			if (a[i] > a[i + 1]) {
				count += (a[i] - a[i + 1]);
				a[i + 1] = a[i];
			}
		}

		System.out.println(count);

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

		for (int i = 0; i < n; i++) {
			a[i] = sc.nextInt();
		}

		for (int i = 0; i < n - 1; i++) {
			if (a[i] > a[i + 1]) {
				count += (a[i] - a[i + 1]);
				a[i + 1] = a[i];
			}
		}

		System.out.println(count);

	}
} public class Main {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		int[] a = new int[n];
		long count = 0L;

		for (int i = 0; i < n; i++) {
			a[i] = sc.nextInt();
		}

		for (int i = 0; i < n - 1; i++) {
			if (a[i] > a[i + 1]) {
				count += (a[i] - a[i + 1]);
				a[i + 1] = a[i];
			}
		}

		System.out.println(count);

	}
} 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];
		long count = 0L;

		for (int i = 0; i < n; i++) {
			a[i] = sc.nextInt();
		}

		for (int i = 0; i < n - 1; i++) {
			if (a[i] > a[i + 1]) {
				count += (a[i] - a[i + 1]);
				a[i + 1] = a[i];
			}
		}

		System.out.println(count);

	}
}