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

const int MAXN = 200010;
const long long INF = 1e18;
long long H[MAXN], r[MAXN], l[MAXN];

int main() {
	int N; long long P;
	cin >> N >> P;
	for (int i=1; i<=N; ++i) cin >> H[i]; 
	r[1] = 0;
	l[1] = INF;
	for (int i=2; i<=N; ++i) { 
		long long new_r = min(r[i-1], l[i-1]) + P;
		long long cont_r = r[i-1] + max(0LL, H[i] - H[i-1]);
		r[i] = min(new_r, cont_r); 
		long long new_l = min(r[i-1], l[i-1]) + P;
		long long cont_l = l[i-1] + max(0LL, H[i-1] - H[i]);
		l[i] = min(new_l, cont_l);
	}
	
	cout << min(r[N], l[N]) << endl;
	return 0;
}