Problem:
Score : 300 points

Problem Statement

N persons are standing in a row. The height of the i-th person from the front is A_i.

We want to have each person stand on a stool of some heights - at least zero - so that the following condition is satisfied for every person:

Condition: Nobody in front of the person is taller than the person. Here, the height of a person includes the stool.

Find the minimum total height of the stools needed to meet this goal.

Constraints

1 \leq N \leq 2\times 10^5

1 \leq A_i \leq 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
A_1 \ldots A_N

Output

Print the minimum total height of the stools needed to meet the goal.

Sample Input 1

5
2 1 5 4 3

Sample Output 1

4

If the persons stand on stools of heights 0, 1, 0, 1, and 2, respectively, their heights will be 2, 2, 5, 5, and 5, satisfying the condition.

We cannot meet the goal with a smaller total height of the stools.

Sample Input 2

5
3 3 3 3 3

Sample Output 2

0

Giving a stool of height 0 to everyone will work.

Solution in Java (OpenJDK 11.0.6) (judge verdict: Accepted)

import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Main {

  public static void main(String[] args) {
    // abc176_a();
    // abc176_b();
    abc176_c();
  }

  private static void abc176_a() {
    try (Scanner sc = new Scanner(System.in)) {
      double nAll = sc.nextInt();
      double xOneTime = sc.nextInt();
      int tMinute = sc.nextInt();

      System.out.println((int) Math.ceil(nAll / xOneTime) * tMinute);

    } catch (Exception e) {
      System.out.println("エラー" + e);
    }
  }

  private static void abc176_b() {
    try (Scanner sc = new Scanner(System.in)) {
      String nValue = sc.next();
      List<Integer> numList = new ArrayList<Integer>();

      for (int i = 1; i <= nValue.length(); i++) {
        numList.add(parseI(nValue.substring(i - 1, i)));
      }

      int sum = 0;

      for (int num : numList) {
        sum += num;
      }

      if (sum % 9 == 0) {
        System.out.println("Yes");
      } else {
        System.out.println("No");
      }

    } catch (Exception e) {
      System.out.println("エラー" + e);
    }
  }

  private static void abc176_c() {
    try (Scanner sc = new Scanner(System.in)) {
      int nPeopleCount = sc.nextInt();
      int[] aTallList = new int[2 * 100000];

      long totalAdd = 0;
      int tall = 0;

      aTallList[0] = parseI(sc.next());
      for (int i = 1; i < nPeopleCount; i++) {
        tall = parseI(sc.next());
        if (0 < aTallList[i - 1] - tall) {
          totalAdd += aTallList[i - 1] - tall;
          tall = aTallList[i - 1];
        }
        aTallList[i] = tall;
      }
      System.out.println(totalAdd);

    } catch (Exception e) {
      System.out.println("エラー" + e);
    }
  }

  // int 2147483648 [ 2 * 10(9)]
  // long 9223372036854775808 [ 9 * 10(18)]

  public static int parseI(String value) {
    return Integer.parseInt(value);
  }

  public static long parseL(String value) {
    return Long.parseLong(value);
  }

  public static double parseD(String value) {
    return Double.parseDouble(value);
  }

  public static <T> String parseS(T value) {
    return String.valueOf(value);
  }

  public static BigDecimal parseBigD(String value) {
    return new BigDecimal(value);
  }

  public static BigInteger parseBigI(String value) {
    return new BigInteger(value);
  }

}