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#include <bits/stdc++.h>
using namespace std;

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

	int n, k;
	cin >> n >> k;
	vector<int> a(n);
	for (int i = 0; i < n; i++)
		cin >> a[i];

	int wynik = 0;
	for (int i = 1; i < n; i++) {
		int dod = max(0, a[i - 1] - a[i] - k);
		wynik += dod;
		a[i] += dod;
	}

	for (int i = n - 2; i >= 0; i--) {
		int dod = max(0, a[i + 1] - a[i] - k);
		wynik += dod;
		a[i] += dod;
	}

	cout << wynik << '\n';
}