#include <bits/stdc++.h>
using namespace std;
long long sqr(long long x) { return x * x; }
int mysqrt(long long x) {
  int l = 0, r = 1e9 + 1;
  while (r - l > 1) {
    int m = (l + r) / 2;
    if (m * (long long)m <= x)
      l = m;
    else
      r = m;
  }
  return l;
}
mt19937 rnd(chrono::high_resolution_clock::now().time_since_epoch().count());
mt19937_64 rndll(
    chrono::high_resolution_clock::now().time_since_epoch().count());
long long AR = 19, BR = 13, CR = 23, XR = 228, YR = 322, MODR = 1e9 + 993;
long long myrand() {
  long long ZR = (XR * AR + YR * BR + CR) % MODR;
  XR = YR;
  YR = ZR;
  return ZR;
}
int gcd(int a, int b) { return a ? gcd(b % a, a) : b; }
int gcdex(int a, int b, int &x, int &y) {
  if (a == 0) {
    x = 0;
    y = 1;
    return b;
  }
  int x1, y1;
  int ret = gcdex(b % a, a, x1, y1);
  x = y1 - (b / a) * x1;
  y = x1;
  return ret;
}
const int Mod = 1e9 + 7;
int Bpow(int x, long long y) {
  int ret = 1;
  int w = x;
  while (y) {
    if (y & 1) ret = (ret * (long long)w) % Mod;
    w = (w * (long long)w) % Mod;
    y >>= 1;
  }
  return ret;
}
int Bdiv(int x) {
  int a, b;
  gcdex(x, Mod, a, b);
  if (a < 0) a += Mod;
  return a;
}
int Bdiv(int x, int y) { return (x * (long long)Bpow(y, Mod - 2)) % Mod; }
inline int ad(int x, int y) { return x + y >= Mod ? x + y - Mod : x + y; }
inline int dif(int x, int y) { return x - y < 0 ? x - y + Mod : x - y; }
inline int mul(int x, int y) { return (x * (long long)y) % Mod; }
int inv(int a) {
  int b = Mod, x = 0, y = 1;
  while (a) {
    int t = b / a;
    b -= a * t;
    x -= t * y;
    swap(a, b);
    swap(x, y);
  }
  if (x < 0) x += Mod;
  return x;
}
void setmin(int &x, int y) { x = min(x, y); }
void setmax(int &x, int y) { x = max(x, y); }
void setmin(long long &x, long long y) { x = min(x, y); }
void setmax(long long &x, long long y) { x = max(x, y); }
const long long llinf = 1e18 + 100;
const long double eps = 1e-9;
const int maxn = 2e5 + 100, maxw = 1e6 + 100, inf = 2e9 + 100, sq = 600, X = 43,
          LG = 17;
int n;
int p[maxn], a[maxn], rnk[maxn];
pair<long long, int> e[maxn];
bool us[maxn];
int get(int x) { return x == p[x] ? x : p[x] = get(p[x]); }
int uni(int x, int y) {
  x = get(x);
  y = get(y);
  if (x == y) return 0;
  if (rnk[x] < rnk[y]) swap(x, y);
  p[y] = x;
  us[y] = 1;
  if (rnk[x] == rnk[y]) rnk[x]++;
  return 1;
}
int D;
long long ans;
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> n >> D;
  for (int i = 0; i < n; i++) cin >> a[i], p[i] = i;
  int eds = 0;
  while (eds < n - 1) {
    for (int i = 0; i < n; i++)
      if (!us[i]) e[i].first = llinf;
    pair<long long, int> x = {llinf, -1}, y = x;
    for (int i = 0; i < n; i++) {
      if (x.second != -1 && x.second != get(i)) {
        e[get(i)] =
            min(e[get(i)], {x.first + i * (long long)D + a[i], x.second});
      } else {
        if (y.second != -1 && y.second != get(i)) {
          e[get(i)] =
              min(e[get(i)], {y.first + i * (long long)D + a[i], y.second});
        }
      }
      pair<long long, int> o = {a[i] - D * (long long)i, get(i)};
      if (x.second == -1 || x.first > o.first) {
        if (x.second != o.second) y = x;
        x = o;
      } else if (y.second == -1 || y > o)
        y = o;
    }
    x = {llinf, -1}, y = x;
    for (int i = n - 1; i >= 0; i--) {
      if (x.second != -1 && x.second != get(i)) {
        e[get(i)] =
            min(e[get(i)], {x.first - i * (long long)D + a[i], x.second});
      } else {
        if (y.second != -1 && y.second != get(i)) {
          e[get(i)] =
              min(e[get(i)], {y.first - i * (long long)D + a[i], y.second});
        }
      }
      pair<long long, int> o = {a[i] + D * (long long)i, get(i)};
      if (x.second == -1 || x.first > o.first) {
        if (x.second != o.second) y = x;
        x = o;
      } else if (y.second == -1 || y > o)
        y = o;
    }
    for (int i = 0; i < n; i++)
      if (!us[i]) {
        long long v = e[i].first;
        int id = e[i].second;
        if (v != llinf && uni(id, i)) {
          eds++;
          ans += v;
        }
      }
  }
  cout << ans;
}
