import java.util.Scanner;

public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();

		long tmp = 0;
		long max = 0;
		long now = 0;
		long result = 0;
		for(int i=0;i < N;i++) {
			now = sc.nextLong();
			if(now > max) {
				max = now;
			}

			if(now < max) {
				result = result + (max - now);
			}
		}

		sc.close();
		System.out.println(result);

	}

} 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 tmp = 0;
		long max = 0;
		long now = 0;
		long result = 0;
		for(int i=0;i < N;i++) {
			now = sc.nextLong();
			if(now > max) {
				max = now;
			}

			if(now < max) {
				result = result + (max - now);
			}
		}

		sc.close();
		System.out.println(result);

	}

} Main public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();

		long tmp = 0;
		long max = 0;
		long now = 0;
		long result = 0;
		for(int i=0;i < N;i++) {
			now = sc.nextLong();
			if(now > max) {
				max = now;
			}

			if(now < max) {
				result = result + (max - now);
			}
		}

		sc.close();
		System.out.println(result);

	} main {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();

		long tmp = 0;
		long max = 0;
		long now = 0;
		long result = 0;
		for(int i=0;i < N;i++) {
			now = sc.nextLong();
			if(now > max) {
				max = now;
			}

			if(now < max) {
				result = result + (max - now);
			}
		}

		sc.close();
		System.out.println(result);

	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = sc.nextInt(); N sc.nextInt() sc.nextInt sc long tmp = 0; tmp 0 long max = 0; max 0 long now = 0; now 0 long result = 0; result 0 for(int i=0;i < N;i++) {
			now = sc.nextLong();
			if(now > max) {
				max = now;
			}

			if(now < max) {
				result = result + (max - now);
			}
		} int i=0; int i=0; i 0 i < N i N i++ i++ i {
			now = sc.nextLong();
			if(now > max) {
				max = now;
			}

			if(now < max) {
				result = result + (max - now);
			}
		} {
			now = sc.nextLong();
			if(now > max) {
				max = now;
			}

			if(now < max) {
				result = result + (max - now);
			}
		} now = sc.nextLong() now sc.nextLong() sc.nextLong sc if(now > max) {
				max = now;
			} now > max now max {
				max = now;
			} max = now max now if(now < max) {
				result = result + (max - now);
			} now < max now max {
				result = result + (max - now);
			} result = result + (max - now) result result + (max - now) result (max - now) max now sc.close() sc.close sc System.out.println(result) System.out.println System.out System System.out result String[] args args public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();

		long tmp = 0;
		long max = 0;
		long now = 0;
		long result = 0;
		for(int i=0;i < N;i++) {
			now = sc.nextLong();
			if(now > max) {
				max = now;
			}

			if(now < max) {
				result = result + (max - now);
			}
		}

		sc.close();
		System.out.println(result);

	}

} public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();

		long tmp = 0;
		long max = 0;
		long now = 0;
		long result = 0;
		for(int i=0;i < N;i++) {
			now = sc.nextLong();
			if(now > max) {
				max = now;
			}

			if(now < max) {
				result = result + (max - now);
			}
		}

		sc.close();
		System.out.println(result);

	}

} 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 tmp = 0;
		long max = 0;
		long now = 0;
		long result = 0;
		for(int i=0;i < N;i++) {
			now = sc.nextLong();
			if(now > max) {
				max = now;
			}

			if(now < max) {
				result = result + (max - now);
			}
		}

		sc.close();
		System.out.println(result);

	}

}