/******************
*  Author: BD747  *
******************/
/*


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*/
#include<algorithm>
#include<cstdio>
#include<iostream>
#include<cstring>
#include<cmath>
#include<map>
#include<queue>
#include<set>
#include<sstream>
#include<stack>
#include<string>
#include<vector>
#include<bits/stdc++.h>
using namespace std;

typedef long long ll;

ll l[200005];
ll ltr[200005];
ll rtl[200005];
ll n,d,ret;

int main(){

	ios_base::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0);
	
	cin>>n>>d;
	for(int i=0;i<n;i++){
		cin>>l[i];
		ret+=l[i];
	}
	ret+=(n-1)*d;
	ltr[0]=l[0];
	for(int i=1;i<n;i++){
		ltr[i]=min(l[i],ltr[i-1]+d);
	}
	rtl[n-1]=l[n-1];
	for(int i=n-2;i>=0;i--){
		rtl[i]=min(l[i],rtl[i+1]+d);
	}
	for(int i=1;i<n-1;i++){
		ret+=min(rtl[i],ltr[i]);
	}
	cout<<ret<<endl;

	return 0;
}


Measured memory_bytes: 4992