import java.util.Scanner;

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

		// 入力値の取得
		int N = sc.nextInt();
		long[] A = new long[N];
		for(int i = 0; i < N; i++) {
			A[i] = sc.nextLong();
		}
		long sum = 0;
		long temp = A[0];
		
		for (int i = 1; i < N; i++) {
			if (A[i] < temp) {
				sum += temp - A[i];
			}
			else {
				temp = A[i];
			}
		}
		// 結果の出力
		System.out.println(sum);
		
		sc.close();
	}
} import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		// 入力値の取得
		int N = sc.nextInt();
		long[] A = new long[N];
		for(int i = 0; i < N; i++) {
			A[i] = sc.nextLong();
		}
		long sum = 0;
		long temp = A[0];
		
		for (int i = 1; i < N; i++) {
			if (A[i] < temp) {
				sum += temp - A[i];
			}
			else {
				temp = A[i];
			}
		}
		// 結果の出力
		System.out.println(sum);
		
		sc.close();
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		// 入力値の取得
		int N = sc.nextInt();
		long[] A = new long[N];
		for(int i = 0; i < N; i++) {
			A[i] = sc.nextLong();
		}
		long sum = 0;
		long temp = A[0];
		
		for (int i = 1; i < N; i++) {
			if (A[i] < temp) {
				sum += temp - A[i];
			}
			else {
				temp = A[i];
			}
		}
		// 結果の出力
		System.out.println(sum);
		
		sc.close();
	} main {
		Scanner sc = new Scanner(System.in);

		// 入力値の取得
		int N = sc.nextInt();
		long[] A = new long[N];
		for(int i = 0; i < N; i++) {
			A[i] = sc.nextLong();
		}
		long sum = 0;
		long temp = A[0];
		
		for (int i = 1; i < N; i++) {
			if (A[i] < temp) {
				sum += temp - A[i];
			}
			else {
				temp = A[i];
			}
		}
		// 結果の出力
		System.out.println(sum);
		
		sc.close();
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = sc.nextInt(); N sc.nextInt() sc.nextInt sc long[] A = new long[N]; A new long[N] N for(int i = 0; i < N; i++) {
			A[i] = sc.nextLong();
		} int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
			A[i] = sc.nextLong();
		} {
			A[i] = sc.nextLong();
		} A[i] = sc.nextLong() A[i] A i sc.nextLong() sc.nextLong sc long sum = 0; sum 0 long temp = A[0]; temp A[0] A 0 for (int i = 1; i < N; i++) {
			if (A[i] < temp) {
				sum += temp - A[i];
			}
			else {
				temp = A[i];
			}
		} int i = 1; int i = 1; i 1 i < N i N i++ i++ i {
			if (A[i] < temp) {
				sum += temp - A[i];
			}
			else {
				temp = A[i];
			}
		} {
			if (A[i] < temp) {
				sum += temp - A[i];
			}
			else {
				temp = A[i];
			}
		} if (A[i] < temp) {
				sum += temp - A[i];
			}
			else {
				temp = A[i];
			} A[i] < temp A[i] A i temp {
				sum += temp - A[i];
			} sum += temp - A[i] sum temp - A[i] temp A[i] A i {
				temp = A[i];
			} temp = A[i] temp A[i] A i System.out.println(sum) System.out.println System.out System System.out sum sc.close() sc.close sc String[] args args public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		// 入力値の取得
		int N = sc.nextInt();
		long[] A = new long[N];
		for(int i = 0; i < N; i++) {
			A[i] = sc.nextLong();
		}
		long sum = 0;
		long temp = A[0];
		
		for (int i = 1; i < N; i++) {
			if (A[i] < temp) {
				sum += temp - A[i];
			}
			else {
				temp = A[i];
			}
		}
		// 結果の出力
		System.out.println(sum);
		
		sc.close();
	}
} public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		// 入力値の取得
		int N = sc.nextInt();
		long[] A = new long[N];
		for(int i = 0; i < N; i++) {
			A[i] = sc.nextLong();
		}
		long sum = 0;
		long temp = A[0];
		
		for (int i = 1; i < N; i++) {
			if (A[i] < temp) {
				sum += temp - A[i];
			}
			else {
				temp = A[i];
			}
		}
		// 結果の出力
		System.out.println(sum);
		
		sc.close();
	}
} Main
import java.util.Scanner;

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

		// 入力値の取得
		int N = sc.nextInt();
		long[] A = new long[N];
		for(int i = 0; i < N; i++) {
			A[i] = sc.nextLong();
		}
		long sum = 0;
		long temp = A[0];
		
		for (int i = 1; i < N; i++) {
			if (A[i] < temp) {
				sum += temp - A[i];
			}
			else {
				temp = A[i];
			}
		}
		// 結果の出力
		System.out.println(sum);
		
		sc.close();
	}
}
