#include <bits/stdc++.h>
using namespace std;
using ll = long long;
template <typename T = int>
struct Rmq {
  vector<T> raw;
  static const int LOG = 17;
  int k;
  int n;
  vector<int> st[LOG];
  Rmq(vector<T> _v) {
    raw = _v;
    n = raw.size();
    k = 32 - __builtin_clz(n);
    for (int j = 0; j < k; j++) {
      st[j].resize(n);
    }
    build();
  }
  inline int comp(int x, int y) { return raw[x] < raw[y] ? x : y; }
  void build() {
    for (int i = 0; i < n; i++) {
      st[0][i] = i;
    }
    for (int j = 1; j < k; j++) {
      for (int i = 0; i + (1 << j) <= n; i++) {
        st[j][i] = comp(st[j - 1][i], st[j - 1][i + (1 << (j - 1))]);
      }
    }
  }
  inline int query_id(int l, int r) {
    assert(0 <= l && l < r && r <= n);
    int j = 31 - __builtin_clz(r - l);
    return comp(st[j][l], st[j][r - (1 << j)]);
  }
  inline T query(int l, int r) { return raw[query_id(l, r)]; }
};
struct Dsu {
  int n;
  vector<int> p;
  Dsu(int _n) {
    n = _n;
    p.resize(n);
    init();
  }
  inline void init() {
    for (int i = 0; i < n; i++) {
      p[i] = i;
    }
  }
  inline int find(int x) { return p[x] == x ? x : p[x] = find(p[x]); }
  inline bool join(int x, int y) {
    x = find(x);
    y = find(y);
    if (x == y) return false;
    p[y] = x;
    return true;
  }
  inline bool check(int x, int y) { return find(x) == find(y); }
};
struct Edge {
  int x, y;
  ll cost;
  Edge() {}
  Edge(int _x, int _y, ll _cost) : x(_x), y(_y), cost(_cost) {}
  bool operator<(const Edge& _oth) const { return cost < _oth.cost; }
};
void solve() {
  int n;
  ll D;
  cin >> n >> D;
  vector<ll> a(n), L(n), R(n);
  for (int i = 0; i < n; i++) {
    ll x;
    cin >> x;
    a[i] = x;
    L[i] = x - i * D;
    R[i] = x + i * D;
  }
  Rmq<ll> mL(L), mR(R);
  vector<Edge> es;
  function<void(int, int)> cut = [&](int l, int r) {
    if (r - l <= 1) return;
    int m = (r + l) / 2;
    int i = mL.query_id(l, m);
    for (int k = m; k < r; k++) {
      es.emplace_back(i, k, R[k] + L[i]);
    }
    int j = mR.query_id(m, r);
    for (int k = l; k < m; k++) {
      es.emplace_back(j, k, L[k] + R[j]);
    }
    cut(l, m);
    cut(m, r);
  };
  cut(0, n);
  sort(es.begin(), es.end());
  Dsu d(n);
  ll res = 0;
  for (auto& e : es) {
    if (!d.check(e.x, e.y)) {
      res += e.cost;
      d.join(e.x, e.y);
    }
  }
  cout << res;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  solve();
  cout << endl;
}
