#include <bits/stdc++.h>
using namespace std;
struct InitAim {
  InitAim() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.precision(12);
    cout << fixed;
  }
} aim_cpo;
template <typename T>
bool chmin(T &a, T b) {
  return a > b ? (a = b, true) : false;
}
template <typename T>
bool chmax(T &a, T b) {
  return a < b ? (a = b, true) : false;
}
template <typename T>
void ln(T i, T n) {
  cout << (i == n - 1 ? "\n" : " ");
}
template <typename T, typename S>
ostream &operator<<(ostream &out, const pair<T, S> &pair1) {
  out << '(' << pair1.first << ", " << pair1.second << ')';
  return out;
}
template <typename T>
ostream &operator<<(ostream &out, const vector<T> &vector1) {
  out << '[';
  for (unsigned int i = 0; i < vector1.size(); i++) {
    out << vector1[i];
    if (i == vector1.size() - 1)
      out << "]";
    else
      out << ", ";
  }
  return out;
}
template <typename T>
T LCM(T a, T b) {
  return a / __gcd(a, b) * b;
}
template <typename T>
T EXTGCD(T a, T b, T &x, T &y) {
  T d = a;
  if (b != 0) {
    d = EXTGCD(b, a % b, y, x);
    y -= (a / b) * x;
  } else
    x = 1, y = 0;
  return d;
}
template <typename T>
bool is_prime(T a) {
  for (int i = 2; i * i <= a; i++)
    if (a % i == 0) return true;
  return false;
}
template <typename T, typename S>
T Pow(T a, S b) {
  T res = 1, now = a;
  while (b) {
    if (b & 1) res *= now;
    b >>= 1;
    now *= now;
  }
  return res;
}
long long MOD = 1000000000LL + 7LL;
class Mint {
 public:
  long long x;
  Mint() : x(0) {}
  Mint(const int x) {
    if (x < MOD && x >= 0)
      this->x = x;
    else
      this->x = (MOD + x % MOD) % MOD;
  }
  Mint(const long long x) {
    if (x < MOD && x >= 0)
      this->x = x;
    else
      this->x = (MOD + x % MOD) % MOD;
  }
  Mint(const Mint &c) { this->x = c.x; }
  Mint &operator=(const int c) {
    if (c < MOD && c >= 0)
      this->x = c;
    else
      this->x = (MOD + c % MOD) % MOD;
    return *this;
  }
  Mint &operator=(const long long c) {
    if (c < MOD && c >= 0)
      this->x = c;
    else
      this->x = (MOD + c % MOD) % MOD;
    return *this;
  }
  Mint &operator=(const Mint c) {
    this->x = c.x;
    return *this;
  }
  bool operator==(const Mint &b) { return x == b.x; }
  bool operator!=(const Mint &b) { return !(x == b.x); }
  bool operator<(const Mint &b) { return x < b.x; }
  bool operator>(const Mint &b) { return x > b.x; }
};
ostream &operator<<(ostream &out, const Mint &mint) {
  out << mint.x;
  return out;
}
istream &operator>>(istream &in, const Mint &mint) {
  in >> mint.x;
  return in;
}
inline Mint add(const Mint a, const Mint b) {
  const long long x = (a.x + b.x) % MOD;
  return Mint(x);
}
inline Mint mul(const Mint a, const Mint b) {
  long long x = (a.x * b.x) % MOD;
  return Mint(x);
}
template <typename T>
Mint ModPow(Mint a, T b) {
  assert(b >= 0);
  Mint res = 1;
  while (b) {
    if (b & 1) res = mul(res, a);
    b >>= 1;
    a = mul(a, a);
  }
  return res;
}
inline Mint ModInverse(const Mint x) {
  long long a = x.x, b = MOD, u = 1, v = 0;
  while (b) {
    long long t = a / b;
    swap(a -= t * b, b);
    swap(u -= t * v, v);
  }
  Mint res(u);
  return res;
}
inline Mint operator-(const Mint x) { return Mint(-x.x); }
inline Mint operator+(const Mint a, const Mint b) { return add(a, b); }
inline Mint operator*(const Mint a, const Mint b) { return mul(a, b); }
inline Mint operator-(const Mint a, const Mint b) { return add(a, -b); }
template <typename T>
inline Mint operator+(const Mint a, const T b) {
  return add(a, Mint(b));
}
template <typename T>
inline Mint operator*(const Mint a, const T b) {
  return mul(a, Mint(b));
}
template <typename T>
inline Mint operator-(const Mint a, const T b) {
  return add(a, Mint(-b));
}
template <typename T>
inline Mint operator/(const Mint a, const T b) {
  return mul(a, ModInverse(Mint(b)));
}
template <typename T>
inline Mint operator^(const Mint a, const T b) {
  return ModPow(a, b);
}
template <typename T>
inline Mint operator+=(Mint &a, const T b) {
  a = a + b;
  return a;
}
template <typename T>
inline Mint operator-=(Mint &a, const T b) {
  a = a - b;
  return a;
}
template <typename T>
inline Mint operator*=(Mint &a, const T b) {
  a = a * b;
  return a;
}
template <typename T>
inline Mint operator/=(Mint &a, const T b) {
  a = a / b;
  return a;
}
template <typename T>
T EulerTotient(T a) {
  vector<pair<int, int>> v;
  for (T i = 2; i * i <= a; i++) {
    int cnt = 0;
    while (a % i == 0) {
      cnt++;
      a /= i;
    }
    if (cnt != 0) v.emplace_back(i, cnt);
  }
  if (a != 1) v.emplace_back(a, 1);
  T res = 1;
  for (int i = 0; i < (int)v.size(); i++) {
    if (v[i].second == 1) {
      res *= v[i].first - 1;
    } else {
      res *= Pow(v[i].first, v[i].second) - Pow(v[i].first, v[i].second - 1);
    }
  }
  return res;
}
template <typename T, typename S>
Mint comb(T a, S b) {
  chmin(b, a - b);
  Mint res = 1LL, now = a;
  for (long long i = 1; i <= b; i++) {
    res *= now;
    res /= i;
    now -= 1;
  }
  return res;
}
template <typename T>
class BIT {
 public:
  BIT(int size) { BITTable.assign(++size, 0); }
  T sum(int k) {
    T res = 0;
    for (++k; k > 0; k -= k & -k) {
      res += BITTable[k];
    }
    return res;
  }
  T sum(int l, int r) {
    if (l == 0) return sum(r);
    return sum(r) - sum(l - 1);
  }
  void update(int k, T x) {
    for (++k; k < (int)BITTable.size(); k += k & -k) BITTable[k] += x;
  }

 private:
  vector<T> BITTable;
};
template <typename T>
class IntervalTree {
  using F = function<T(T, T)>;

 public:
  IntervalTree(int n, const F func, const T init) : func(func), init(init) {
    size = 1;
    while ((int)size < n) size <<= 1;
    table.assign(2 * size, init);
  }
  void set(int k, T &x) { table[size + k] = x; }
  void build() {
    for (int i = size - 1; i >= 0; --i) {
      table[i] = func(table[i * 2], table[i * 2 + 1]);
    }
  }
  void update(int k, const T &x) {
    k += size;
    table[k] = x;
    while (k >>= 1) {
      table[k] = func(table[k * 2], table[k * 2 + 1]);
    }
  }
  T query(int a, int b) {
    T L = init, R = init;
    for (a += size, b += size; a < b; a >>= 1, b >>= 1) {
      if (a & 1) L = func(L, table[a++]);
      if (b & 1) R = func(table[--b], R);
    }
    return func(L, R);
  }
  T operator[](const int k) const { return table[k + size]; }

 private:
  unsigned int size;
  vector<T> table;
  const F func;
  const T init;
};
class UnionFind {
 public:
  explicit UnionFind(int _n) : n(_n) {
    par.resize(static_cast<unsigned long>(_n));
    rank.resize(static_cast<unsigned long>(_n));
    sizes.resize(static_cast<unsigned long>(_n));
    for (int i = 0; i < _n; i++) {
      par[i] = i;
      rank[i] = 0;
      sizes[i] = 1;
    }
  }
  int find(int a) {
    if (par[a] == a) return a;
    return par[a] = find(par[a]);
  }
  bool same(int a, int b) { return find(a) == find(b); }
  void unite(int a, int b) { link(find(a), find(b)); }
  int size(int a) { return sizes[find(a)]; }
  void view() {
    for (int i = 0; i < n; i++) {
      cout << " par"
           << "[" << i << "]=" << par[i] << ((i == n - 1) ? "\n" : ",");
    }
    for (int i = 0; i < n; i++) {
      cout << "size"
           << "[" << i << "]=" << sizes[i] << ((i == n - 1) ? "\n" : ",");
    }
    cout << "\n";
  }

 private:
  void link(int a, int b) {
    if (same(a, b)) return;
    if (rank[a] > rank[b]) {
      par[b] = a;
      sizes[a] += sizes[b];
      sizes[b] = 0;
    } else {
      par[a] = b;
      if (rank[a] == rank[b]) rank[b]++;
      sizes[b] += sizes[a];
      sizes[a] = 0;
    }
  }
  int n;
  vector<int> par;
  vector<int> rank;
  vector<int> sizes;
};
template <typename T>
class Dinic {
 public:
  Dinic(int SIZE) : SIZE(SIZE) {
    v = vector<vector<tuple<int, T, int>>>(SIZE + 10);
  }
  void AddEdge(int from, int to, T cap) {
    v[from].push_back(make_tuple(to, cap, v[to].size()));
    v[to].push_back(make_tuple(from, 0, v[from].size() - 1));
  }
  void bfs(int s) {
    level = vector<int>(SIZE + 10, -1);
    queue<int> q;
    level[s] = 0;
    q.push(s);
    while (!q.empty()) {
      int now = q.front();
      q.pop();
      for (int i = 0; i < (int)v[now].size(); i++) {
        int next, nextrv;
        T nextc;
        tie(next, nextc, nextrv) = v[now][i];
        if (nextc > 0 && level[next] < 0) {
          level[next] = level[now] + 1;
          q.push(next);
        }
      }
    }
  }
  T dfs(int now, int t, T f) {
    if (now == t) return f;
    for (int &i = iter[now]; i < (int)v[now].size(); i++) {
      int next, nextrv;
      T nextc;
      tie(next, nextc, nextrv) = v[now][i];
      if (nextc > 0 && level[now] < level[next]) {
        T d = dfs(next, t, min(f, nextc));
        if (d > 0) {
          get<1>(v[now][i]) -= d;
          get<1>(v[next][nextrv]) += d;
          return d;
        }
      }
    }
    return 0;
  }
  T max_flow(int s, int t) {
    T flow = 0;
    for (;;) {
      bfs(s);
      if (level[t] < 0) return flow;
      iter = vector<int>(SIZE + 10, 0);
      int f;
      while ((f = dfs(s, t, INT_MAX)) > 0) {
        flow += f;
      }
    }
  }

 private:
  int SIZE;
  vector<vector<tuple<int, T, int>>> v;
  vector<int> level, iter;
};
template <typename flow_t, typename cost_t>
struct PrimalDual {
  const cost_t INF;
  struct edge {
    int to;
    flow_t cap;
    cost_t cost;
    int rev;
    bool isrev;
  };
  vector<vector<edge>> graph;
  vector<cost_t> potential, min_cost;
  vector<int> prevv, preve;
  PrimalDual(int V) : graph(V), INF(numeric_limits<cost_t>::max()) {}
  void add_edge(int from, int to, flow_t cap, cost_t cost) {
    graph[from].emplace_back(
        (edge){to, cap, cost, (int)graph[to].size(), false});
    graph[to].emplace_back(
        (edge){from, 0, -cost, (int)graph[from].size() - 1, true});
  }
  cost_t min_cost_flow(int s, int t, flow_t f) {
    int V = (int)graph.size();
    cost_t ret = 0;
    using Pi = pair<cost_t, int>;
    priority_queue<Pi, vector<Pi>, greater<Pi>> que;
    potential.assign(V, 0);
    preve.assign(V, -1);
    prevv.assign(V, -1);
    while (f > 0) {
      min_cost.assign(V, INF);
      que.emplace(0, s);
      min_cost[s] = 0;
      while (!que.empty()) {
        Pi p = que.top();
        que.pop();
        if (min_cost[p.second] < p.first) continue;
        for (int i = 0; i < graph[p.second].size(); i++) {
          edge &e = graph[p.second][i];
          cost_t nextCost = min_cost[p.second] + e.cost + potential[p.second] -
                            potential[e.to];
          if (e.cap > 0 && min_cost[e.to] > nextCost) {
            min_cost[e.to] = nextCost;
            prevv[e.to] = p.second, preve[e.to] = i;
            que.emplace(min_cost[e.to], e.to);
          }
        }
      }
      if (min_cost[t] == INF) return -1;
      for (int v = 0; v < V; v++) potential[v] += min_cost[v];
      flow_t addflow = f;
      for (int v = t; v != s; v = prevv[v]) {
        addflow = min(addflow, graph[prevv[v]][preve[v]].cap);
      }
      f -= addflow;
      ret += addflow * potential[t];
      for (int v = t; v != s; v = prevv[v]) {
        edge &e = graph[prevv[v]][preve[v]];
        e.cap -= addflow;
        graph[v][e.rev].cap += addflow;
      }
    }
    return ret;
  }
  void output() {
    for (int i = 0; i < graph.size(); i++) {
      for (auto &e : graph[i]) {
        if (e.isrev) continue;
        auto &rev_e = graph[e.to][e.rev];
        cout << i << "->" << e.to << " (flow: " << rev_e.cap << "/"
             << rev_e.cap + e.cap << ")"
             << "\n";
      }
    }
  }
};
template <typename T>
using Matrix = vector<vector<T>>;
template <typename T>
void init(int h, int w, Matrix<T> &matrix) {
  matrix = vector<vector<T>>(h, vector<T>(w));
}
template <typename T>
Matrix<T> &operator*(Matrix<T> &matrix, Matrix<T> &matrix1) {
  int height = (int)matrix.size();
  int width = (int)matrix[0].size();
  int height2 = (int)matrix1.size();
  int width2 = (int)matrix1[0].size();
  assert(width == height2);
  Matrix<T> res;
  res = vector<vector<T>>(height, vector<T>(width2, 0));
  for (int i = 0; i < height; i++) {
    for (int j = 0; j < width2; j++) {
      for (int k = 0; k < width; k++) {
        res[i][j] += matrix[i][k] * matrix1[k][j];
      }
    }
  }
  matrix.swap(res);
  return matrix;
}
template <typename T>
Matrix<T> Pow(Matrix<T> matrix, long long x) {
  Matrix<T> res = vector<vector<T>>(matrix.size(), vector<T>(matrix.size(), 0));
  for (int i = 0; i < (int)matrix.size(); i++) {
    res[i][i] = 1;
  }
  while (x) {
    if (x & 1) {
      res = res * matrix;
    }
    matrix = matrix * matrix;
    x >>= 1;
  }
  return res;
}
int n;
long long d;
long long a[200001];
vector<tuple<int, int, long long>> v;
int main() {
  cin >> n >> d;
  for (auto i = (0); i < (n); ++i) cin >> a[i];
  function<void(int, int)> rec = [&](int begin, int end) {
    ;
    ;
    if (end - begin <= 1) return;
    int mid = (begin + end) / 2;
    long long leftmin = LLONG_MAX;
    long long rightmin = LLONG_MAX;
    int leftminid = -1, rightminid = -1;
    for (auto i = (begin); i < (mid); ++i) {
      if (chmin(leftmin, -i * d + a[i])) leftminid = i;
    }
    for (auto i = (mid); i < (end); ++i) {
      if (chmin(rightmin, i * d + a[i])) rightminid = i;
    }
    for (auto i = (begin); i < (mid); ++i) {
      long long cost = (rightminid - i) * d + a[i] + a[rightminid];
      v.push_back(make_tuple(cost, i, rightminid));
    }
    for (auto i = (mid); i < (end); ++i) {
      long long cost = (i - leftminid) * d + a[i] + a[leftminid];
      v.push_back(make_tuple(cost, i, leftminid));
    }
    rec(begin, mid);
    rec(mid, end);
  };
  rec(0, n);
  UnionFind uf(n);
  sort((v).begin(), (v).end());
  long long ans = 0;
  for (auto i = (0); i < ((int)v.size()); ++i) {
    long long cost;
    int from, to;
    tie(cost, from, to) = v[i];
    assert(cost > 0);
    if (uf.same(from, to)) continue;
    ans += cost;
    uf.unite(from, to);
  }
  cout << ans << "\n";
  return 0;
}
