#include <iostream>
#include <vector>
#include <string>
#include <cmath>
#include <algorithm>
#include <utility>
#include <queue>
#include <set>
#include <map>

using namespace std;
typedef  long long ll;
typedef pair<int,int> PII;
typedef vector<int> VI;
typedef vector<VI> VVI;
#define  MP make_pair
#define  PB push_back
#define inf  1000000007

ll dp1[200010],dp2[200010];

int main(){
	int n;
	cin >> n;
	ll p;
	cin >> p;
	vector<ll> v(n);
	for(int i=0;i<n;i++){
		cin >> v[i];
	}
	dp1[0]=0;
	dp2[0]=p;
	for(int i=1;i<n;i++){
		dp1[i] = min(dp1[i-1]+p,min(dp1[i-1]+max(v[i]-v[i-1],(ll)0),dp2[i-1]+p));
		dp2[i] = min(dp2[i-1]+p,min(dp2[i-1]+max(v[i-1]-v[i],(ll)0),dp1[i-1]+p));
	}
	cout << min(dp1[n-1],dp2[n-1]) << endl;
	return 0;
}