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 C++ (GCC 9.2.1) (judge verdict: Runtime Error)

//#pragma region ALL(include define etc)
#include <iostream>   // swap(a, b)
#include <string>
#include <cmath>      // abs(絶対値) sin cos tan(角度 / 180.0 * 3.141592)
#include <vector>     // vec.push_back(a) vec.pop_back()
#include <algorithm>  // max(a, b) min(a, b) reverse() sort()
#include <functional> // sort(a, a + N, greater<型>());
#include <limits>
#include <math.h>
#include <iomanip>
#define int long long
//#define int unsigned long long
#define ll long long
#define double long double
using namespace std;
//#pragma endregion

signed main()
{
	// 10^18 = 1000000000000000000

	//int h1, h2, m1, m2, k;
	//int box, box1,box2;

	//int N;
	int n;
	//char n;
	//int a, b, c;
	//int m;
	int h, w, x;
	int k;
	int d;
	//int t;
	//string s;
	//string t;
	//int m1, m2;
	//int a, b, c, k;
	//int x, y;

	string s;
	//string s[100000];
	//string c[7];
	//int a[100000];
	//int b[200000];
	//int a[2000000] = { 0 };
	//int b[2000000] = { 0 };
	//int a[20000] = { 0 };
	//int b[20000] = { 0 };
	//vector<int>a(2000000);
	//vector<int>b(2000000);

	//int aaa = 0;
	//int bbb = 0;

	//int box[20000] = { 0 };
	char box[20000];
	int a[20000] = { 0 };
	//int box = 0;
	//int box[7][7] = { 0 };
	//int box2;
	//int p[1111];
	//int x[2000], y[2000];
	//int l[100];


	//long double aaa;

	int count = 0;
	//int k, d;
	//int a = 0;
	int all = 0;
	//double all;
	//double a, b;
	//double h, m;
	//int a[30000] = { 0 };
	//double c, d, e;

	//double mbox, hbox;
	//double box, box2;

	bool flag = true;
	//bool flag = false;

	//string str;

	//cin >> h1 >> m1 >> h2 >> m2 >> k;
	cin >> n;
	//cin >> a >> b >> c;
	//cin >> s;
	//cin >> h >> w >> k;
	//cin >> n >> x >> t;

	for (int i = 0; i < n; i++)
	{
		cin >> a[i];
	}

	/*for (int i = 0;i<n; i++)
	{
		if (i == 0)
		{

		}
		else
		{
			for (int j = 0; a[i - 1] > a[i]; j++)
			{
				a[i]++;
				all++;
			}
		}
	}*/

	for (int i = 1; i < n; i++)
	{
		if (a[i - 1] > a[i])
		{
			all += (a[i - 1] - a[i]);
			a[i] = a[i - 1];
		}
	}

	//getline(cin, s);

	/*for (int i = 0; i < count; i++)
	{
		all += s[i] - '0';
	}*/

	//n = s.length();

	//sort(p, p + n);
	//n = n - 'Z';

	//box = n % 26;

	//for (int i = 0; i < k; i++)
	//{
	//	all += p[i];
	//}

	//all = n + (n * n) + (n * n * n);

	/*if (n > 0)
	{
		cout << "a\n";
	}
	else
	{
		cout << "A\n";
	}*/
	//n = t.length();

	/*cout << "AC x " << ac << "\n";
	cout << "WA x " << wa << "\n";
	cout << "TLE x " << tle << "\n";
	cout << "RE x " << re << "\n";*/

	//cout << x << "\n";
	cout << all << "\n";
	//cout << box << "\n";
	//cout << a << b << c << "\n";

	/*if (flag == true)
	{
		cout << "Yes\n";
	}
	else
	{
		cout << "No\n";
	}*/

	//cout << fixed << setprecision(111) << all;
	//return 0;
}