#include <bits/stdc++.h>
#pragma GCC diagnostic ignored "-Wunused-result"
#pragma GCC diagnostic ignored "-Wunused-function"
using namespace std;
namespace {
namespace unolight {
template <class T>
void _R(T &x) {
  cin >> x;
}
void _R(int &x) { scanf("%d", &x); }
void _R(int64_t &x) { scanf("%" PRId64, &x); }
void _R(double &x) { scanf("%lf", &x); }
void _R(char &x) { scanf(" %c", &x); }
void _R(char *x) { scanf("%s", x); }
void R() {}
template <class T, class... U>
void R(T &head, U &...tail) {
  _R(head);
  R(tail...);
}
template <class T>
void _W(const T &x) {
  cout << x;
}
void _W(const int &x) { printf("%d", x); }
void _W(const int64_t &x) { printf("%" PRId64, x); }
void _W(const double &x) { printf("%.16f\n", x); }
void _W(const char &x) { putchar(x); }
void _W(const char *x) { printf("%s", x); }
template <class T>
void _W(const vector<T> &x) {
  for (auto i = x.begin(); i != x.end(); _W(*i++))
    if (i != x.cbegin()) putchar(' ');
}
void W() {}
template <class T, class... U>
void W(const T &head, const U &...tail) {
  _W(head);
  putchar(sizeof...(tail) ? ' ' : '\n');
  W(tail...);
}
template <class T>
inline bool chmax(T &a, const T &b) {
  return b > a ? a = b, true : false;
}
template <class T>
inline bool chmin(T &a, const T &b) {
  return b < a ? a = b, true : false;
}
template <class T>
using MaxHeap = priority_queue<T>;
template <class T>
using MinHeap = priority_queue<T, vector<T>, greater<T>>;
template <class T, class F = less<T>>
void sort_uniq(vector<T> &v, F f = F()) {
  sort(begin(v), end(v), f);
  v.resize(unique(begin(v), end(v)) - begin(v));
}
const int N = 200010;
int n, D, A[N];
multiset<pair<int64_t, pair<int, int>>> s;
int64_t f(int a, int b) {
  if (a > b) swap(a, b);
  return (int64_t)(b - a) * D + A[a] + A[b];
}
void solve(int l, int r) {
  if (l + 1 == r) return;
  solve(l, (l + r) / 2);
  solve((l + r) / 2, r);
  int m = (l + r) / 2;
  int x, y;
  {
    int64_t mi = 1e18;
    for (int i = l; i < m; i++) {
      int64_t me = (int64_t)-D * i + A[i];
      if (chmin(mi, me)) x = i;
    }
  }
  {
    int64_t mi = 1e18;
    for (int i = m; i < r; i++) {
      int64_t me = (int64_t)D * i + A[i];
      if (chmin(mi, me)) y = i;
    }
  }
  for (int i = m; i < r; i++) {
    s.insert({f(x, i), {x, i}});
  }
  for (int i = l; i < m; i++) {
    s.insert({f(i, y), {i, y}});
  }
}
struct UnionFind {
  int n, num;
  vector<int> sz, par;
  UnionFind() {}
  UnionFind(int n_) : n(n_), num(n_), sz(n_, 1), par(n_, 0) {
    iota(par.begin(), par.end(), 0);
  }
  int find(int x) { return x == par[x] ? x : par[x] = find(par[x]); }
  bool same(int x, int y) { return find(x) == find(y); }
  void unite(int x, int y) {
    x = find(x);
    y = find(y);
    if (x == y) return;
    if (sz[x] < sz[y]) swap(x, y);
    sz[x] += sz[y];
    par[y] = x;
    num--;
  }
  int size(int x) { return sz[find(x)]; }
  int count() const { return num; }
};
void main() {
  R(n, D);
  for (int i = 0; i < int(n); i++) R(A[i]);
  solve(0, n);
  int64_t ans = 0;
  UnionFind uf(n);
  while (((int)(s).size())) {
    int64_t w = s.begin()->first;
    int u = s.begin()->second.first, v = s.begin()->second.second;
    if (!uf.same(u, v)) {
      ans += w;
      uf.unite(u, v);
    }
    s.erase(s.begin());
  }
  W(ans);
}
}  // namespace unolight
}  // namespace
int main() {
  unolight::main();
  return 0;
}
