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

typedef long long LL;

void resolve(vector<LL>& heights, int pos, LL k, LL& res) {
	if (pos == -1)
		return;

	if (heights[pos] > heights[pos+1] + k) {
		LL diff = heights[pos] - k - heights[pos+1];
		heights[pos+1] += diff;
		res += diff;
	} else if (heights[pos] + k < heights[pos+1]) {
		LL diff = heights[pos+1] - k - heights[pos];
		heights[pos] += diff;
		res += diff;
		resolve(heights, pos-1, k, res);
	}
}

int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
	cout.tie(nullptr);

	LL n, k;
	cin >> n >> k;

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

	LL res = 0;

	for (int i = 0; i < n-1; ++i) {
		resolve(heights, i, k, res);
	}

	cout << res << '\n';

	return 0;
}