CF205B.Little Elephant and Sorting

The Little Elephant loves sortings.

He has an array a consisting of n integers. Let's number the array elements from 1 to n, then the i-th element will be denoted as a__i. The Little Elephant can make one move to choose an arbitrary pair of integers l and r (1 ≤ l ≤ r ≤ n) and increase a__i by 1 for all i such that l ≤ i ≤ r.

Help the Little Elephant find the minimum number of moves he needs to convert array a to an arbitrary array sorted in the non-decreasing order. Array a, consisting of n elements, is sorted in the non-decreasing order if for any i (1 ≤ i < n) a__i ≤ a__i + 1 holds.

小象喜欢排序。

他有一个由 $n$ 个整数组成的数组 $a$。我们将数组元素从 $1$ 编号到 $n$，则第 $i$ 个元素记为 $a_i$。小象每次操作可以任选一对整数 $l$ 和 $r$（满足 $1 \leq l \leq r \leq n$），并对所有满足 $l \leq i \leq r$ 的下标 $i$，将 $a_i$ 增加 $1$。

请帮助小象找出：将数组 $a$ 变为任意一个非递减排序数组所需的最少操作次数。一个含 $n$ 个元素的数组 $a$ 被称为非递减排序的，当且仅当对任意 $i$（$1 \leq i < n$）均满足 $a_i \leq a_{i+1}$。

The first line contains a single integer n (1 ≤ n ≤ 105) — the size of array a. The next line contains n integers, separated by single spaces — array a (1 ≤ a__i ≤ 109). The array elements are listed in the line in the order of their index's increasing.

第一行包含一个整数 $n$（$1 \leq n \leq 10^5$）—— 数组 $a$ 的大小。
下一行包含 $n$ 个整数，以单个空格分隔 —— 数组 $a$（$1 \leq a_i \leq 10^9$）。
数组元素按其下标递增的顺序在该行中列出。

In a single line print a single integer — the answer to the problem.

Please, do not use the %lld specifier to read or write 64-bit integers in С++. It is preferred to use the cin, cout streams or the %I64d specifier.

在一行中输出一个整数——即该问题的答案。

请注意，在 C++ 中读取或写入 64 位整数时，请勿使用 %lld 说明符。推荐使用 cin、cout 流，或 %I64d 说明符。

In the first sample the array is already sorted in the non-decreasing order, so the answer is 0.

In the second sample you need to perform two operations: first increase numbers from second to third (after that the array will be: [3, 3, 2]), and second increase only the last element (the array will be: [3, 3, 3]).

In the third sample you should make at least 6 steps. The possible sequence of the operations is: (2; 3), (2; 3), (2; 3), (3; 3), (3; 3), (3; 3). After that the array converts to [7, 7, 7, 47].

在第一个样例中，数组已经按非递减顺序排好序，因此答案为 0。

在第二个样例中，你需要执行两次操作：第一次将第 2 个到第 3 个元素全部增加（操作后数组变为：[3, 3, 2]），第二次仅增加最后一个元素（操作后数组变为：[3, 3, 3]）。

在第三个样例中，你至少需要进行 6 步操作。一种可能的操作序列是：(2; 3), (2; 3), (2; 3), (3; 3), (3; 3), (3; 3)。操作完成后，数组变为 [7, 7, 7, 47]。