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#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>

using namespace std;

int main()
{
	cin.tie(0);
	ios::sync_with_stdio(0);

	int n, k;
	cin >> n >> k;

	vector<int> data(n);
	for (auto& e : data)cin >> e;

	int min_v = data[0] - k;
	int res{};

	//prawe zbocze
	for (int i = 1; i < n; ++i)
	{
		if (data[i] < min_v)
		{
			res += min_v - data[i];
			data[i] = min_v;
		}

		min_v = data[i] - k;
	}

	min_v = data.back() - k;

	//lewe
	for (int i = n - 2; i >= 0; --i)
	{
		if (data[i] < min_v)
		{
			res += min_v - data[i];
			data[i] = min_v;
		}

		min_v = data[i] - k;
	}

	cout << res;
}