#define _CRT_SECURE_NO_WARNINGS
#define _SCL_SECURE_NO_WARNINGS
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cassert>
#include <iostream>
#include <string>
#include <vector>
#include <list>
#include <utility>
#include <algorithm>
#include <functional>
#include <cmath>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <iomanip>
#include <sstream>
#include <bitset>
#include <limits>
#include <numeric>
#include <valarray>
#include <fstream>

using namespace std;
typedef unsigned int uint;
typedef long long LL;
typedef unsigned long long ULL;
typedef pair<LL, LL> PP;
#define REP(i, a, n) for(LL i = (a), i##_max = (n); i < i##_max; ++i)
#define REM(i, a, n) for(LL i = (LL)(n) - 1, i##min = (a); i >= i##min; --i)
#define ALL(arr) (arr).begin(), (arr).end()
#define FLOAT fixed << setprecision(16)
#define SPEEDUP {cin.tie(NULL); ios::sync_with_stdio(false);}
const int INF = 0x3FFFFFFF;
const LL INFLL = 0x3FFFFFFF3FFFFFFF;
const double INFD = 1.0e+308;
const string INFSTR = "\x7f";
const double EPS = 1.0e-9;

void YesNo(bool b) { cout << (b ? "Yes" : "No") << endl; }
void YESNO(bool b) { cout << (b ? "YES" : "NO") << endl; }
template <class T, class U>
istream& operator>>(istream& ist, pair<T, U>& right) { return ist >> right.first >> right.second; }
template <class T, class U>
ostream& operator<<(ostream& ost, const pair<T, U>& right) { return ost << right.first << ' ' << right.second; }
template <class T, class TCompatible, size_t N>
void Fill(T(&dest)[N], const TCompatible& val) { fill(dest, dest + N, val); }
template <class T, class TCompatible, size_t M, size_t N>
void Fill(T(&dest)[M][N], const TCompatible& val) { for (int i = 0; i < M; ++i) Fill(dest[i], val); }
template<class T>
T Compare(T left, T right) { return left > right ? 1 : (left < right ? -1 : 0); }
istream& Ignore(istream& ist) { string s; ist >> s; return ist; }
bool Inside(int i, int j, int h, int w) { return i >= 0 && i < h && j >= 0 && j < w; }
template <class T>
T Next() { T buf; cin >> buf; return buf; }

#ifdef ONLY_MY_ENVIR
#include "IntMod.h"
#include "UnionFind.h"
#include "Graph.h"
#include "Range.h"
#include "Global.h"
#include "FlowSolver.h"
#include "Tree.h"
#include "SuffixArray.h"
#include "Geometry.h"
#include "Matrix.h"
#include "SegmentTree.h"
#include "SegmentTree2D.h"
#include "BIT.h"
#include "Rational.h"
#include "Position.h"
#include "Factorization.h"
#include "Math.h"
#endif

#ifdef __GNUC__
typedef __int128 LLL;
istream& operator>> (istream& ist, __int128& val) { LL tmp;  ist >> tmp; val = tmp; return ist; }
ostream& operator<< (ostream& ost, __int128 val) { LL tmp = val; ost << tmp; return ost; }
#endif

#if 1234567891
#include <array>
#include <random>
#include <unordered_set>
#include <unordered_map>
template<typename T>
using PriorityQ = priority_queue<T, vector<T>, greater<T> >;
// template <class T>
// auto Is(const T& value) { return [value](const auto& comparand) -> bool { return comparand == value; }; }
#endif

struct MinimumPP {
	using Type = PP;
	static Type Identity() {
		return PP(INFLL, INFLL);
	}
	static Type Operate(const Type& left, const Type& right) {
		return left < right ? left : right;
	}
};


LL N, D;
LL A[200000];
SegmentTree<MinimumPP> Asc(18);
SegmentTree<MinimumPP> Dsc(18);


const LL Huge = INFLL;
int main() {
	cin >> N >> D;
	REP(i, 0, N) {
		cin >> A[i];
		Asc.Update(i, PP(A[i] + i * D, i));
		Dsc.Update(i, PP(A[i] - i * D, i));
	}
	
	LL sum = 0;
	PriorityQ<pair<LL, PP>> Q;
	auto mn = Asc.Query(1, N);
	Q.push(make_pair(mn.first + A[0], PP(0, mn.second)));
	Asc.Update(0, PP(Huge, 0));
	Dsc.Update(0, PP(Huge, 0));

	int cnt = 1;
	while (cnt < N) {
		auto p = Q.top(); Q.pop();
		LL cost = p.first;
		int from = p.second.first;
		int to = p.second.second;

		if (Asc.Get(to).first >= Huge) {
			auto mn = Asc.Query(from + 1, N) - PP(D * from, 0);
			mn = min(mn, Dsc.Query(0, from) + PP(D * from, 0));

			Q.push(make_pair(mn.first + A[from], PP(from, mn.second)));
			continue;
		}

		Asc.Update(to, PP(Huge, to));
		Dsc.Update(to, PP(Huge, to));
		++cnt;
		sum += cost;

		auto mn2 = Asc.Query(from + 1, N) - PP(D * from, 0);
		mn2 = min(mn2, Dsc.Query(0, from) + PP(D * from, 0));
		Q.push(make_pair(mn2.first + A[from], PP(from, mn2.second)));

		auto mn = Asc.Query(to + 1, N) - PP(D * to, 0);
		mn = min(mn, Dsc.Query(0, to) + PP(D * to, 0));
		Q.push(make_pair(mn.first + A[to], PP(to, mn.second)));

	}
	cout << sum << endl;
	return 0;
}

#define _CRT_SECURE_NO_WARNINGS
#define _SCL_SECURE_NO_WARNINGS
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cassert>
#include <iostream>
#include <string>
#include <vector>
#include <list>
#include <utility>
#include <algorithm>
#include <functional>
#include <cmath>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <iomanip>
#include <sstream>
#include <bitset>
#include <limits>
#include <numeric>
#include <valarray>
#include <fstream>

using namespace std;
typedef unsigned int uint;
typedef long long LL;
typedef unsigned long long ULL;
typedef pair<LL, LL> PP;
#define REP(i, a, n) for(LL i = (a), i##_max = (n); i < i##_max; ++i)
#define REM(i, a, n) for(LL i = (LL)(n) - 1, i##min = (a); i >= i##min; --i)
#define ALL(arr) (arr).begin(), (arr).end()
#define FLOAT fixed << setprecision(16)
#define SPEEDUP {cin.tie(NULL); ios::sync_with_stdio(false);}
const int INF = 0x3FFFFFFF;
const LL INFLL = 0x3FFFFFFF3FFFFFFF;
const double INFD = 1.0e+308;
const string INFSTR = "\x7f";
const double EPS = 1.0e-9;

void YesNo(bool b) { cout << (b ? "Yes" : "No") << endl; }
void YESNO(bool b) { cout << (b ? "YES" : "NO") << endl; }
template <class T, class U>
istream& operator>>(istream& ist, pair<T, U>& right) { return ist >> right.first >> right.second; }
template <class T, class U>
ostream& operator<<(ostream& ost, const pair<T, U>& right) { return ost << right.first << ' ' << right.second; }
template <class T, class TCompatible, size_t N>
void Fill(T(&dest)[N], const TCompatible& val) { fill(dest, dest + N, val); }
template <class T, class TCompatible, size_t M, size_t N>
void Fill(T(&dest)[M][N], const TCompatible& val) { for (int i = 0; i < M; ++i) Fill(dest[i], val); }
template<class T>
T Compare(T left, T right) { return left > right ? 1 : (left < right ? -1 : 0); }
istream& Ignore(istream& ist) { string s; ist >> s; return ist; }
bool Inside(int i, int j, int h, int w) { return i >= 0 && i < h && j >= 0 && j < w; }
template <class T>
T Next() { T buf; cin >> buf; return buf; }

#ifdef ONLY_MY_ENVIR
#include "IntMod.h"
#include "UnionFind.h"
#include "Graph.h"
#include "Range.h"
#include "Global.h"
#include "FlowSolver.h"
#include "Tree.h"
#include "SuffixArray.h"
#include "Geometry.h"
#include "Matrix.h"
#include "SegmentTree.h"
#include "SegmentTree2D.h"
#include "BIT.h"
#include "Rational.h"
#include "Position.h"
#include "Factorization.h"
#include "Math.h"
#endif

#ifdef __GNUC__
typedef __int128 LLL;
istream& operator>> (istream& ist, __int128& val) { LL tmp;  ist >> tmp; val = tmp; return ist; }
ostream& operator<< (ostream& ost, __int128 val) { LL tmp = val; ost << tmp; return ost; }
#endif

#if 1234567891
#include <array>
#include <random>
#include <unordered_set>
#include <unordered_map>
template<typename T>
using PriorityQ = priority_queue<T, vector<T>, greater<T> >;
// template <class T>
// auto Is(const T& value) { return [value](const auto& comparand) -> bool { return comparand == value; }; }
#endif

struct MinimumPP {
	using Type = PP;
	static Type Identity() {
		return PP(INFLL, INFLL);
	}
	static Type Operate(const Type& left, const Type& right) {
		return left < right ? left : right;
	}
};


LL N, D;
LL A[200000];
SegmentTree<MinimumPP> Asc(18);
SegmentTree<MinimumPP> Dsc(18);


const LL Huge = INFLL;
int main() {
	cin >> N >> D;
	REP(i, 0, N) {
		cin >> A[i];
		Asc.Update(i, PP(A[i] + i * D, i));
		Dsc.Update(i, PP(A[i] - i * D, i));
	}
	
	LL sum = 0;
	PriorityQ<pair<LL, PP>> Q;
	auto mn = Asc.Query(1, N);
	Q.push(make_pair(mn.first + A[0], PP(0, mn.second)));
	Asc.Update(0, PP(Huge, 0));
	Dsc.Update(0, PP(Huge, 0));

	int cnt = 1;
	while (cnt < N) {
		auto p = Q.top(); Q.pop();
		LL cost = p.first;
		int from = p.second.first;
		int to = p.second.second;

		if (Asc.Get(to).first >= Huge) {
			auto mn = Asc.Query(from + 1, N) - PP(D * from, 0);
			mn = min(mn, Dsc.Query(0, from) + PP(D * from, 0));

			Q.push(make_pair(mn.first + A[from], PP(from, mn.second)));
			continue;
		}

		Asc.Update(to, PP(Huge, to));
		Dsc.Update(to, PP(Huge, to));
		++cnt;
		sum += cost;

		auto mn2 = Asc.Query(from + 1, N) - PP(D * from, 0);
		mn2 = min(mn2, Dsc.Query(0, from) + PP(D * from, 0));
		Q.push(make_pair(mn2.first + A[from], PP(from, mn2.second)));

		auto mn = Asc.Query(to + 1, N) - PP(D * to, 0);
		mn = min(mn, Dsc.Query(0, to) + PP(D * to, 0));
		Q.push(make_pair(mn.first + A[to], PP(to, mn.second)));

	}
	cout << sum << endl;
	return 0;
}