#include <bits/stdc++.h>
using namespace std;
#ifndef ONLINE_JUDGE
	#include <boost/multiprecision/cpp_int.hpp>
	#include <boost/multiprecision/cpp_dec_float.hpp>
	using bll = boost::multiprecision::cpp_int;
	using bdouble = boost::multiprecision::cpp_dec_float_100;
#endif
#ifdef LOCAL_DEV
	void debug_impl() { std::cerr << std::endl; }
	template<typename Head, typename... Tail> void debug_impl(Head head, Tail... tail) { std::cerr << " " << head << (sizeof...(tail) ? "," : ""); debug_impl(tail...); }
	#define debug(...) { std::cerr << std::boolalpha << "(" << #__VA_ARGS__ << ") ="; debug_impl(__VA_ARGS__); std::cerr << std::noboolalpha; }
#else
	#define debug(...) {}
#endif
#ifdef LOCAL_TEST
	#define BOOST_STACKTRACE_USE_ADDR2LINE
	#define BOOST_STACKTRACE_ADDR2LINE_LOCATION /usr/local/opt/binutils/bin/addr2line
	#define _GNU_SOURCE
	#include <boost/stacktrace.hpp>
	namespace std {
		template<typename T> class dvector : public std::vector<T> {
		public:
			dvector() : std::vector<T>() {}
			explicit dvector(size_t n, const T& value = T()) : std::vector<T>(n, value) {}
			dvector(const std::vector<T>& v) : std::vector<T>(v) {}
			dvector(const std::initializer_list<T> il) : std::vector<T>(il) {}
			dvector(const typename std::vector<T>::iterator first, const typename std::vector<T>::iterator last) : std::vector<T>(first, last) {}
			dvector(const std::string::iterator first, const std::string::iterator last) : std::vector<T>(first, last) {}
			T& operator[](size_t n) {
				try { return this->at(n); } catch (const std::exception& e) {
					std::cerr << boost::stacktrace::stacktrace() << std::endl; return this->at(n);
				}
			}
			const T& operator[](size_t n) const {
				try { return this->at(n); } catch (const std::exception& e) {
					std::cerr << boost::stacktrace::stacktrace() << std::endl; return this->at(n);
				}
			}
		};
	}
	class dbool {
	private:
		bool boolvalue;
	public:
		dbool() : boolvalue(false) {}
		dbool(bool b) : boolvalue(b) {}
		dbool(const dbool &b) : boolvalue(b.boolvalue) {}
		operator bool&() { return boolvalue; }
		operator const bool&() const { return boolvalue; }
	};
	template<typename T> std::ostream& operator<<(std::ostream& s, const dvector<T>& v) {
		for (int i = 0, len = v.size(); i < len; ++i){ s << v[i]; if (i < len - 1) s << "\t"; } return s; }
	template<typename T> std::ostream& operator<<(std::ostream& s, const dvector< dvector<T> >& vv) {
		for (int i = 0, len = vv.size(); i < len; ++i){ s << vv[i] << std::endl; } return s; }
	template<typename T> std::ostream& operator<<(std::ostream& s, const std::set<T>& se) {
		s << "{ "; for (auto itr = se.begin(); itr != se.end(); ++itr){ s << (*itr) << "\t"; } s << "}"; return s; }
	template<typename T> std::ostream& operator<<(std::ostream& s, const std::multiset<T>& se) {
		s << "{ "; for (auto itr = se.begin(); itr != se.end(); ++itr){ s << (*itr) << "\t"; } s << "}"; return s; }
	template<typename T1, typename T2> std::ostream& operator<<(std::ostream& s, const std::map<T1, T2>& m) {
		s << "{" << std::endl; for (auto itr = m.begin(); itr != m.end(); ++itr){ s << "\t" << (*itr).first << " : " << (*itr).second << std::endl; } s << "}"; return s; }
	template<typename T1, typename T2> std::ostream& operator<<(std::ostream& s, const std::pair<T1, T2>& p) { 
		return s << "(" << p.first << ", " << p.second << ")"; }
	#define vector dvector
	#define bool dbool
	class SIGFPE_exception : std::exception {};
	class SIGSEGV_exception : std::exception {};
	void catch_SIGFPE(int e) { std::cerr << boost::stacktrace::stacktrace() << std::endl; throw SIGFPE_exception();	}
	void catch_SIGSEGV(int e) { std::cerr << boost::stacktrace::stacktrace() << std::endl; throw SIGSEGV_exception(); }
	signed convertedmain();
	signed main() { signal(SIGFPE, catch_SIGFPE); signal(SIGSEGV, catch_SIGSEGV); return convertedmain(); }
	#define main() convertedmain()
#endif
//#define int long long
using ll = long long;
//constexpr int INF = 1e9;//INT_MAX=(1<<31)-1=2147483647
constexpr ll INF = (ll)1e18;//(1LL<<63)-1=9223372036854775807
constexpr ll MOD = (ll)1e9 + 7;
constexpr double EPS = 1e-9;
constexpr ll dx[4] = {1LL, 0LL, -1LL, 0LL};
constexpr ll dy[4] = {0LL, 1LL, 0LL, -1LL};
constexpr ll dx8[8] = {1LL, 0LL, -1LL, 0LL, 1LL, 1LL, -1LL, -1LL};
constexpr ll dy8[8] = {0LL, 1LL, 0LL, -1LL, 1LL, -1LL, 1LL, -1LL};
#define rep(i, n)   for(ll i=0, i##_length=(n); i< i##_length; ++i)
#define repeq(i, n) for(ll i=1, i##_length=(n); i<=i##_length; ++i)
#define rrep(i, n)   for(ll i=(n)-1; i>=0; --i)
#define rrepeq(i, n) for(ll i=(n)  ; i>=1; --i)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
void p() { std::cout << '\n'; }
template<typename Head, typename... Tail> void p(Head head, Tail... tail) { std::cout << head << (sizeof...(tail) ? " " : ""); p(tail...); }
template<typename T> inline void pv(std::vector<T> &v) { for(ll i=0, N=v.size(); i<N; i++) std::cout << v[i] << " \n"[i==N-1]; }
template<typename T> inline T gcd(T a, T b) { return b ? gcd(b,a%b) : a; }
template<typename T> inline T lcm(T a, T b) { return a / gcd(a,  b) * b; }
template<typename T> inline bool chmax(T &a, T b) { return a < b && (a = b, true); }
template<typename T> inline bool chmin(T &a, T b) { return a > b && (a = b, true); }
template<typename T> inline void uniq(std::vector<T> &v) { v.erase(unique(v.begin(), v.end()), v.end()); }

/*-----8<-----template-----8<-----*/

class Edge {
public:
	ll from,to,cost;
	Edge() {}
	Edge(ll from, ll to, ll cost) : from(from), to(to), cost(cost) {}
};
ostream& operator<<(ostream& s, const Edge& e) {
	s << "{ " << e.from << " -> " << e.to << ", " << e.cost << " }";
	return s;
}

class UnionFind {
public:
	vector<ll> v;
	UnionFind(size_t size) : v(size, -1) {}

	ll root(ll x) {
		return (v[x] < 0 ? x : v[x] = root(v[x]));
	}

	bool is_root(ll x) {
		return x == root(x);
	}

	bool is_same(ll x, ll y) {
		return root(x) == root(y);
	}

	bool unite(ll x, ll y) {
		x = root(x);
		y = root(y);
		if (x == y) return false;
		if (v[x] > v[y]) swap(x, y);
		v[x] += v[y];
		v[y] = x;
		return true;
	}

	ll size(ll x) {
		return -v[root(x)];
	}
};

/*
グラフ上のボロノイ図を作る 要Edge,UnionFind
引数
　g:探索するグラフ
　startv:探索するスタートノード番号の集合
戻り値
  vector<Edge>: ボロノイ図で接しているセルの情報
    e.from,e.to = 接しているセルの2ノード
    e.cost = e.from-e.to間の距離, 接点までの位置は÷2してください
*/
vector<Edge> voronoi(vector<vector<Edge>> &g, vector<ll> &startv){
	priority_queue<Edge, vector<Edge>, function<bool(Edge,Edge)>> que(
		[](const Edge &x, const Edge &y){
			return x.cost != y.cost ? (x.cost > y.cost) : 
				(x.from != y.from ? x.from < y.from : x.to < y.to);
		}
	);
	for(ll v : startv){
		que.push(Edge(v, v, 0));
	}

	vector<ll> dist(g.size(), INF);
	vector<ll> prev(g.size(), -1);
	UnionFind u(g.size());
	vector<Edge> ans;
	while(!que.empty()){
		Edge e = que.top();
		que.pop();
		if(dist[e.to] == INF){
			dist[e.to] = e.cost;
			prev[e.to] = e.from;
			for(Edge f : g[e.to]){
				que.push(Edge(e.from, f.to, e.cost + f.cost));
			}
		}else{
			if(!u.is_same(e.from, prev[e.to])){
				//prev[e.to] と e.from が出会った
				ans.emplace_back(e.from, prev[e.to], dist[e.to] + e.cost);
				u.unite(e.from, prev[e.to]);
			}
		}
	}
	return ans;
}


////

/*
計算量：O(ElogE)
引数
　g:探索するグラフ
戻り値
　return:最小全域木を構成する辺のコストの総和
　ming:最小全域木のグラフ
*/
ll kruskal(const vector<vector<Edge>> &g, vector<vector<Edge>> &ming) {
	ll n = g.size();
	ming.assign(n, vector<Edge>());
 	UnionFind uf(n);
	priority_queue<Edge, vector<Edge>, function<bool(Edge,Edge)>> que(
		[](const Edge &x, const Edge &y){
			return x.cost != y.cost ? (x.cost > y.cost) : 
				(x.from != y.from ? x.from < y.from : x.to < y.to);
		}
	);
	for(ll u=0; u<n; u++){
		for(Edge e:g[u]){
			if (u < e.to) que.push(e);
		}
	}

	ll edgecount = 0;
	ll mincost = 0;
	while (edgecount < n-1 && !que.empty()) {
		Edge e = que.top();
		que.pop();
		if (uf.unite(e.from, e.to)) {
			edgecount++;
			ming[e.from].push_back(e);
			mincost += e.cost;
		}
	}
	return mincost;
}

/*-----8<-----library-----8<-----*/

ll N, D;
vector<ll> A;

void solve() {
	scanf("%lld%lld", &N, &D);
	A.assign(N, 0);
	rep(i, N) { scanf("%lld", &A[i]); }
	
	vector<vector<Edge>> g(2*N);
	rep(i,N){
		Edge e(i, N+i, A[i]);
		g[e.from].push_back(e);
		Edge f(N+i, i, A[i]);
		g[f.from].push_back(f);
	}
	rep(i,N-1){
		Edge e(N+i, N+i+1, D);
		g[e.from].push_back(e);
		Edge f(N+i+1, N+i, D);
		g[f.from].push_back(f);
	}

	vector<ll> startv;
	rep(i,N)startv.push_back(i);
	vector<Edge> volg = voronoi(g, startv);


	vector<vector<Edge>> g2(N);
	for(Edge e : volg){
		Edge f1(e.from, e.to, abs(e.from-e.to)*D+A[e.from]+A[e.to]);
		g2[f1.from].push_back(f1);
		Edge f2(e.to, e.from, abs(e.from-e.to)*D+A[e.from]+A[e.to]);
		g2[f2.from].push_back(f2);
	}

	vector<vector<Edge>> ming;
	ll mincost = kruskal(g2, ming);
	printf("%lld\n", mincost);
}

// https://atcoder.jp/contests/keyence2019/tasks/keyence2019_e
// 参考：http://tokoharuland.hateblo.jp/entry/2018/04/01/155743
//      http://koba-e964.hatenablog.com/entry/2019/01/14/200541
signed main() {
	solve();
	return 0;
}


Measured memory_bytes: 88044