import java.util.Scanner;

public class Main {

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

		for (int i = 0; i < N; i++) {
			A[i] = sc.nextLong();
		}

		sc.close();

		//
		long result = 0;
		for (int i = 1; i < N; i++) {
			if (A[i - 1] <= A[i]) {
				// result = result;
			} else {
				result = result + (A[i - 1] - A[i]);
				A[i] = A[i - 1];
			}
		}
		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[] A = new long[N];

		for (int i = 0; i < N; i++) {
			A[i] = sc.nextLong();
		}

		sc.close();

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

		for (int i = 0; i < N; i++) {
			A[i] = sc.nextLong();
		}

		sc.close();

		//
		long result = 0;
		for (int i = 1; i < N; i++) {
			if (A[i - 1] <= A[i]) {
				// result = result;
			} else {
				result = result + (A[i - 1] - A[i]);
				A[i] = A[i - 1];
			}
		}
		System.out.println(result);
	} main {
		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		long[] A = new long[N];

		for (int i = 0; i < N; i++) {
			A[i] = sc.nextLong();
		}

		sc.close();

		//
		long result = 0;
		for (int i = 1; i < N; i++) {
			if (A[i - 1] <= A[i]) {
				// result = result;
			} else {
				result = result + (A[i - 1] - A[i]);
				A[i] = A[i - 1];
			}
		}
		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[] 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 sc.close() sc.close sc long result = 0; result 0 for (int i = 1; i < N; i++) {
			if (A[i - 1] <= A[i]) {
				// result = result;
			} else {
				result = result + (A[i - 1] - A[i]);
				A[i] = A[i - 1];
			}
		} int i = 1; int i = 1; i 1 i < N i N i++ i++ i {
			if (A[i - 1] <= A[i]) {
				// result = result;
			} else {
				result = result + (A[i - 1] - A[i]);
				A[i] = A[i - 1];
			}
		} {
			if (A[i - 1] <= A[i]) {
				// result = result;
			} else {
				result = result + (A[i - 1] - A[i]);
				A[i] = A[i - 1];
			}
		} if (A[i - 1] <= A[i]) {
				// result = result;
			} else {
				result = result + (A[i - 1] - A[i]);
				A[i] = A[i - 1];
			} A[i - 1] <= A[i] A[i - 1] A i - 1 i 1 A[i] A i {
				// result = result;
			} {
				result = result + (A[i - 1] - A[i]);
				A[i] = A[i - 1];
			} result = result + (A[i - 1] - A[i]) result result + (A[i - 1] - A[i]) result (A[i - 1] - A[i]) A[i - 1] A i - 1 i 1 A[i] A i A[i] = A[i - 1] A[i] A i A[i - 1] A i - 1 i 1 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[] A = new long[N];

		for (int i = 0; i < N; i++) {
			A[i] = sc.nextLong();
		}

		sc.close();

		//
		long result = 0;
		for (int i = 1; i < N; i++) {
			if (A[i - 1] <= A[i]) {
				// result = result;
			} else {
				result = result + (A[i - 1] - A[i]);
				A[i] = A[i - 1];
			}
		}
		System.out.println(result);
	}
} public class Main {

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

		for (int i = 0; i < N; i++) {
			A[i] = sc.nextLong();
		}

		sc.close();

		//
		long result = 0;
		for (int i = 1; i < N; i++) {
			if (A[i - 1] <= A[i]) {
				// result = result;
			} else {
				result = result + (A[i - 1] - A[i]);
				A[i] = A[i - 1];
			}
		}
		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[] A = new long[N];

		for (int i = 0; i < N; i++) {
			A[i] = sc.nextLong();
		}

		sc.close();

		//
		long result = 0;
		for (int i = 1; i < N; i++) {
			if (A[i - 1] <= A[i]) {
				// result = result;
			} else {
				result = result + (A[i - 1] - A[i]);
				A[i] = A[i - 1];
			}
		}
		System.out.println(result);
	}
}
