#include<iostream>
#include<algorithm>
#include<string>
#include<vector>
#include<cmath>
#include<queue>
#include<functional>
#include<map>
using namespace std;
long long dp[200009][2], n, p, a[200009];
int main() {
	cin >> n >> p;
	for (int i = 1; i <= n; i++)cin >> a[i];
	for (int i = 0; i <= n + 1; i++) { dp[i][0] = (1LL << 60); dp[i][1] = (1LL << 60); }
	dp[1][0] = 0;
	for (int i = 1; i < n; i++) {
		dp[i + 1][0] = min(dp[i + 1][0], dp[i][0] + p);
		dp[i + 1][1] = min(dp[i + 1][1], dp[i][0] + p);
		dp[i + 1][0] = min(dp[i + 1][0], dp[i][1] + p);
		dp[i + 1][1] = min(dp[i + 1][1], dp[i][1] + p);
		dp[i + 1][0] = min(dp[i + 1][0], dp[i][0] + max(0LL, a[i + 1] - a[i]));
		dp[i + 1][1] = min(dp[i + 1][1], dp[i][1] + max(0LL, a[i] - a[i + 1]));
	}
	cout << min(dp[n][0], dp[n][1]) << endl;
	return 0;
}