#include <bits/stdc++.h>
using namespace std;
using vint = vector<long long>;
using vvint = vector<vint>;
using pint = pair<long long, long long>;
using vpint = vector<pint>;
template <typename T>
using priority_queue_rev = priority_queue<T, vector<T>, greater<T>>;
constexpr double PI = 3.1415926535897932384626433832795028;
constexpr long long DY[9] = {0, 1, 0, -1, 1, 1, -1, -1, 0};
constexpr long long DX[9] = {1, 0, -1, 0, 1, -1, -1, 1, 0};
long long sign(long long x) { return (x > 0) - (x < 0); }
long long gcd(long long a, long long b) {
  while (b) {
    swap(a %= b, b);
  }
  return a;
}
long long lcm(long long a, long long b) { return a / gcd(a, b) * b; }
long long cdiv(long long a, long long b) { return (a - 1 + b) / b; }
template <typename T>
void fin(T mes) {
  cout << mes << endl;
  exit(0);
}
template <typename T, typename U>
bool chmax(T &a, const U &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T, typename U>
bool chmin(T &a, const U &b) {
  if (b < a) {
    a = b;
    return true;
  }
  return false;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, const pair<T, U> &rhs) {
  os << "(" << rhs.first << ", " << rhs.second << ")";
  return os;
}
template <typename T>
ostream &operator<<(ostream &os, const vector<T> &rhs) {
  os << "{";
  for (auto itr = rhs.begin(); itr != rhs.end(); itr++) {
    os << *itr << (next(itr) != rhs.end() ? ", " : "");
  }
  os << "}";
  return os;
}
template <typename T>
ostream &operator<<(ostream &os, const deque<T> &rhs) {
  os << "{";
  for (auto itr = rhs.begin(); itr != rhs.end(); itr++) {
    os << *itr << (next(itr) != rhs.end() ? ", " : "");
  }
  os << "}";
  return os;
}
template <typename T>
ostream &operator<<(ostream &os, const set<T> &rhs) {
  os << "{";
  for (auto itr = rhs.begin(); itr != rhs.end(); itr++) {
    os << *itr << (next(itr) != rhs.end() ? ", " : "");
  }
  os << "}";
  return os;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, const map<T, U> &rhs) {
  os << "{";
  for (auto itr = rhs.begin(); itr != rhs.end(); itr++) {
    os << *itr << (next(itr) != rhs.end() ? ", " : "");
  }
  os << "}";
  return os;
}
struct setup {
  static constexpr long long PREC = 20;
  setup() {
    cout << fixed << setprecision(PREC);
    cerr << fixed << setprecision(PREC);
  };
} setup;
struct union_find_tree {
  std::vector<long long> par, size;
  union_find_tree(long long n) : par(n), size(n) {
    for (long long i = 0; i < n; i++) {
      par[i] = i;
      size[i] = 1;
    }
  }
  long long get_root(long long i) {
    if (par[i] == i) {
      return i;
    } else {
      return par[i] = get_root(par[i]);
    }
  }
  void unite(long long i, long long j) {
    if ((i = get_root(i)) == (j = get_root(j))) {
      return;
    }
    if (size[i] < size[j]) {
      std::swap(i, j);
    }
    par[j] = i;
    size[i] += size[j];
  }
  bool are_same(long long i, long long j) { return get_root(i) == get_root(j); }
  long long get_size(long long i) { return size[get_root(i)]; }
};
signed main() {
  long long N, D;
  cin >> N >> D;
  vint A(N), L(N), R(N);
  for (long long i = 0; i < (long long)(N); i++) {
    cin >> A[i], L[i] = A[i] - i * D, R[i] = A[i] + i * D;
  }
  union_find_tree uf(N);
  vector<tuple<long long, long long, long long>> edges;
  long long lmin = 0, rmin = N - 1;
  for (long long i = 1; i < N; i++) {
    edges.emplace_back(L[lmin] + R[i], lmin, i);
    if (L[i] < L[lmin]) {
      lmin = i;
    }
  }
  for (long long i = N - 2; i >= 0; i--) {
    edges.emplace_back(L[i] + R[rmin], i, rmin);
    if (R[i] < R[rmin]) {
      rmin = i;
    }
  }
  sort((edges).begin(), (edges).end());
  long long ans = 0;
  for (auto [w, u, v] : edges) {
    if (!uf.are_same(u, v)) {
      ans += w, uf.unite(u, v);
    }
  }
  cout << ans << endl;
}
