#include <iostream>
#include <algorithm>
using namespace std;
int n, p, a[200009];
int main() {
	cin >> n >> p;
	for (int i = 0; i < n; i++) cin >> a[i];
	long long lm = 0, rm = 1LL << 60;
	for (int i = 1; i < n; i++) {
		long long v = min(lm, rm) + p;
		lm = min(v, lm + max(a[i] - a[i - 1], 0));
		rm = min(v, rm + max(a[i - 1] - a[i], 0));
	}
	cout << min(lm, rm) << endl;
	return 0;
}