#include<bits/stdc++.h>
#define int long long
using namespace std;
const int N=1000010;
const int mod=998244353;
typedef long long ll;
int n,m,p;
int a[N];
int dp[N];
vector<pair<int,int> >v;
signed main(){
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	// freopen("even.in","r",stdin);
	// freopen("even.out","w",stdout);
	cin>>n>>p;
	for(int i=1;i<=n;i++)cin>>a[i];
	int pre=1;
	for(int i=1;i<=n;i++){
		if(i>1&&a[i]<a[i-1]){
			v.push_back(make_pair(pre,i-1));
			pre=i;
		}
	}
	v.push_back(make_pair(pre,n));
	m=v.size();
	for(int i=0;i<m-1;i++){
		int l=v[i].first;
		int r=v[i].second;
		if(l==r){
			dp[i+1]=dp[i];
			continue;
		}
		if(l+1==r){
			dp[i+1]=min(dp[i]+a[r]-a[l],dp[i]+p);
			continue;
		}
		dp[i+1]=min(dp[i]+a[r]-a[l],dp[i]+2*p);
	}
	int l=v.back().first;
	int r=v.back().second;
	if(l==r){
		cout<<dp[m-1]<<"\n";
		return 0;
	}
	if(l+1==r){
		cout<<dp[m-1]+min(a[r]-a[l],p)<<"\n";
		return 0;
	}
	cout<<dp[m-1]+min(a[r]-a[l],p)<<"\n";
	return 0;
}
/*

*/