#include <bits/stdc++.h>

using namespace std;

#define DEBUG(x) cerr<<#x<<": "<<x<<endl;
#define DEBUG_VEC(v) cerr<<#v<<":";for(int i=0;i<v.size();i++) cerr<<" "<<v[i]; cerr<<endl

typedef long long ll;
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
#define pii pair<int,int>
#define pis pair<int,string>
#define psi pair<string,int>
#define pll pair<ll,ll>
template<class S, class T> pair<S, T> operator+(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first + t.first, s.second + t.second); }
template<class S, class T> pair<S, T> operator-(const pair<S, T> &s, const pair<S, T> &t) { return pair<S, T>(s.first - t.first, s.second - t.second); }
template<class S, class T> ostream& operator<<(ostream& os, pair<S, T> p) { os << "(" << p.first << ", " << p.second << ")"; return os; }
#define X first
#define Y second
#define rep(i,n) for(int i=0;i<(n);i++)
#define rep1(i,n) for(int i=1;i<=(n);i++)
#define rrep(i,n) for(int i=(n)-1;i>=0;i--)
#define rrep1(i,n) for(int i=(n);i>0;i--)
#define REP(i,a,b) for(int i=a;i<b;i++)
#define in(x, a, b) (a <= x && x < b)
#define all(c) c.begin(),c.end()
template<class T> bool chmax(T &a, const T &b) { if (a<b) { a = b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a = b; return 1; } return 0; }
#define UNIQUE(v) v.erase(std::unique(v.begin(), v.end()), v.end());
const ll inf = 1000000001;
const ll INF = 1e18;
const ll MOD = 1000000007;
//const ll MOD = 998244353;
const double pi = 3.14159265358979323846;
#define Sp(p) cout<<setprecision(15)<< fixed<<p<<endl;
int dx[4] = { 1,0, -1,0 }, dy[4] = { 0,1,0,-1 };
int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 };
#define fio() cin.tie(0); ios::sync_with_stdio(false);
//#define mp make_pair

class UnionFind {
public:
	int n;
	vi par; //親
	vi ran; //木の深さ
	vi num; //要素数

	UnionFind(int _n) {
		n = _n;
		par.resize(n); ran.resize(n); num.resize(n);
		for (int i = 0; i < n; i++) {
			par[i] = i; ran[i] = 0; num[i] = 1;
		}
	}

	//木の根を求める
	int find(int x) {
		if (par[x] == x) {
			return x;
		}
		else {
			return par[x] = find(par[x]);
		}
	}

	//xとyの属する集合を併合
	void unite(int x, int y) {
		x = find(x); y = find(y);
		int numsum = num[x] + num[y];
		if (x == y) {
			return;
		}
		if (ran[x]<ran[y]) {
			par[x] = y;
		}
		else {
			par[y] = x;
			if (ran[x] == ran[y]) {
				ran[x]++;
			}
		}
		num[x] = num[y] = numsum;
	}

	//xとyが同じ集合に属するか否か
	bool same(int x, int y) {
		return find(x) == find(y);
	}

};

vl a(200020);
vector<pair<ll, pll> > edges;

ll kruskal(int n) {
	sort(edges.begin(), edges.end());
	UnionFind uf(n);
	ll res = 0;
	for (int i = 0; i < edges.size(); i++) {
		if (!uf.same(edges[i].second.first, edges[i].second.second)) {
			uf.unite(edges[i].second.first, edges[i].second.second);
			res += edges[i].first;
		}
	}
	return res;
}


void solve(int l, int r, ll d) {
  if (r - l <= 1) return;
  int m = (l + r) / 2;
  ll mi1 = INF, mi2 = INF;
  int mii1 = -1, mii2 = -1;
  for (int i = l; i < m; i++) {
    if (mi1 > a[i] - d*i) {
      mi1 = a[i] - d*i;
      mii1 = i;
    }
  }
  for (int i = m; i < r; i++) {
    if (mi2 > a[i] + d*i) {
      mi2 = a[i] + d*i;
      mii2 = i;
    }
  }
  for (int i = l; i < m; i++) {
    edges.push_back({a[i] + a[mii2] + (mii2 - i)*d, pii(i, mii2)});
  }
  for (int i = m; i < r; i++) {
    edges.push_back({a[i] + a[mii1] + (i - mii1)*d, pii(mii1, i)});
  }
  solve(l, m, d); solve(m, r, d);
}

int main() {
  fio();
  ll n, d;
  cin >> n >> d;
  rep (i, n) {
    cin >> a[i];
  }
  solve(0, n, d);
  cout << kruskal(n) << endl;
}


Measured memory_bytes: 102240