#include <bits/stdc++.h>
using namespace std;
const int maxn = 200200;
int u[maxn];
long long best[maxn], who[maxn];
vector<int> guys[maxn];
void init() {
  for (int i = 0; i < maxn; i++) u[i] = i;
}
int find(int x) {
  if (x == u[x]) return x;
  return u[x] = find(u[x]);
}
int main() {
  int n;
  long long d;
  cin >> n >> d;
  vector<int> a(n);
  for (int& i : a) cin >> i;
  init();
  int comp = n;
  long long ans = 0;
  while (comp != 1) {
    for (int i = 0; i < n; i++)
      guys[i].clear(), best[i] = 1ll << 62, who[i] = -1;
    multiset<pair<long long, int> > smallest;
    for (int i = 0; i < n; i++) {
      int id = find(i);
      for (int v : guys[id])
        smallest.erase(smallest.find(make_pair(-d * v + a[v], v)));
      if (!smallest.empty()) {
        pair<long long, int> myBest = *smallest.begin();
        long long realCost = d * i + a[i] + myBest.first;
        if (best[id] > realCost) {
          best[id] = realCost;
          who[id] = myBest.second;
        }
      }
      guys[id].push_back(i);
      for (int v : guys[id]) smallest.insert(make_pair(-d * v + a[v], v));
    }
    smallest.clear();
    for (int i = 0; i < n; i++) guys[i].clear();
    for (int i = n - 1; i >= 0; i--) {
      int id = find(i);
      for (int v : guys[id])
        smallest.erase(smallest.find(make_pair(d * v + a[v], v)));
      if (!smallest.empty()) {
        pair<long long, int> myBest = *smallest.begin();
        long long realCost = -d * i + a[i] + myBest.first;
        if (best[id] > realCost) {
          best[id] = realCost;
          who[id] = myBest.second;
        }
      }
      guys[id].push_back(i);
      for (int v : guys[id]) smallest.insert(make_pair(d * v + a[v], v));
    }
    for (int i = 0; i < n; i++)
      if (who[i] != -1) {
        int id = find(i), idWho = find(who[i]);
        if (id != idWho) {
          ans += best[id];
          u[id] = idWho;
          comp--;
        }
      }
  }
  cout << ans << endl;
  return 0;
}
