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.

The first line contains a single integer $n$ $(1<=n<=10^{5})$ — the size of array $a$ . The next line contains $n$ integers, separated by single spaces — array $a$ $(1<=a_{i}<=10^{9})$ . The array elements are listed in the line in the order of their index's increasing.

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.

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].