#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <set>
#include <map>
#include <unordered_map>
#include <unordered_set>
#include <bitset>
#include <algorithm>
#include <cmath>
#include <queue>
#include <stack>
#include <deque>
#include <cassert>
#include <complex>
#include <iomanip>
#include <random>

using namespace std;

typedef long long ll;
#define int ll

int M = 998244353;
#define msum(a, b) ((a) + (b) >= M ? (a) + (b) - M : (a) + (b))
#define msub(a, b) ((a) - (b) < 0 ? (a) - (b) + M : (a) - (b))
#define mmult(a, b) (((a) * (b)) % M)

typedef unsigned long long ull;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<pii> vpi;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<short> vs;
typedef vector<vs> vvs;
typedef vector<vvs> vvvs;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<vvl> vvvl;
typedef vector<ld> vld;
typedef vector<vld> vvld;
typedef vector<vvld> vvvld;
typedef vector<string> vst;
typedef vector<vst> vvst;
typedef pair<ld, ld> pld;
typedef complex<double> base;
typedef complex<int> point;

#define inmin(a, b) a = min(a, (b))
#define inmax(a, b) a = max(a, (b))
#define ALL(a) a.begin(),a.end()
#define RALL(a) a.rbegin(),a.rend()
#define sqr(x) ((x) * (x))
#define fori(i, n) for(int i = 0; i < int(n); ++i)
#define SZ(a) ((int)((a).size()))
#define triple(T) tuple<T, T, T>
#define quad(T) tuple<T, T, T, T>


#define cerr cout
#define watch(x) cerr << (#x) << " = " << (x)    << endl;

const double PI = 2 * acos(0.0);

const string DIGITS = "0123456789";
const string ALPH = "abcdefghijklmnopqrstuvwxyz";

template <class T0, class T1>
inline ostream & operator << (ostream &out, pair<T0, T1> &a) {
	return out << "{" << a.first << ", " << a.second << "}";
}

template <class T0, class T1, class T2>
inline ostream & operator << (ostream &out, tuple<T0, T1, T2> &a) {
	return out << "{" << get<0>(a) << ", " << get<1>(a) << ", " << get<2>(a) << "}";
}

template <class T0, class T1, class T2, class T3>
inline ostream & operator << (ostream &out, tuple<T0, T1, T2, T3> &a) {
	return out << "{" << get<0>(a) << ", " << get<1>(a) << ", " << get<2>(a) << ", " << get<3>(a) << "}";
}

template<class T>
inline ostream & operator << (ostream &out, vector<T> &a) {
	out << "[";
	fori(i, a.size())
		out << a[i] << vector<string>{", ", "]  "}[i + 1 == a.size()];
	return out;
}

void smain();

signed main() {
	ios::sync_with_stdio(0);
	cin.tie(0); cout.tie(0);


	cout << setprecision(12) << fixed;
	smain();
}

#define N 400000
const int oo = 1e18;

int n, d;
int a[N];

int kek(int i, int j)
{
	return abs(j - i) * d + a[j];
}


void smain() {


	cin >> n >> d;

	vi l(n), r(n);


	int ans = (n - 1) * d;

	for (int i = 0; i < n; i++)
	{
		cin >> a[i];
		ans += 2 * a[i];
	}
	ans -= a[0];
	ans -= a[n - 1];

	int mn = oo, v = -1;
	for (int i = 0; i < n; i++)
	{
		l[i] = v;
		int u = (n - i) * d + a[i];
		if (u < mn)
		{
			mn = u;
			v = i;
		}
	}

	mn = oo; v = -1;
	for (int i = n - 1; i >= 0; i--)
	{
		r[i] = v;
		int u = (i + 1) * d + a[i];
		if (u < mn)
		{
			mn = u;
			v = i;
		}
	}

	for (int i = 1; i < n - 1; i++)
	{
		int pr = a[i];

		int nw = min(kek(i, l[i]), kek(i, r[i]));

		if (nw < pr)
			ans -= pr - nw;
	}

	cout << ans;
}

//m1.codeforces.com, m2.codeforces.com или m3.codeforces.com

Measured memory_bytes: 4992