#include <bits/stdc++.h>
using namespace std;
long long mod = 1000000007;
long long mod2 = 998244353;
long long mod3 = 1000003;
long long mod4 = 998244853;
long long mod5 = 1000000009;
long long inf = 1LL << 62;
double pi = 3.141592653589793238462643383279L;
double eps = 1e-14;
int dh[4] = {1, -1, 0, 0};
int dw[4] = {0, 0, 1, -1};
int ddh[8] = {-1, -1, -1, 0, 0, 1, 1, 1};
int ddw[8] = {-1, 0, 1, -1, 1, -1, 0, 1};
struct custom_hash {
  static uint64_t splitmix64(uint64_t x) {
    x += 0x9e3779b97f4a7c15;
    x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
    x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
    return x ^ (x >> 31);
  }
  size_t operator()(uint64_t x) const {
    static const uint64_t FIXED_RANDOM =
        chrono::steady_clock::now().time_since_epoch().count();
    return splitmix64(x + FIXED_RANDOM);
  }
};
long long gcd(long long a, long long b) {
  if (a < b) swap(a, b);
  if (b == 0) return a;
  if (a % b == 0) return b;
  return gcd(b, a % b);
}
long long lcm(long long a, long long b) {
  long long c = gcd(a, b);
  return a * b / c;
}
long long Pow(long long n, long long k) {
  long long ret = 1;
  long long now = n;
  while (k > 0) {
    if (k & 1) ret *= now;
    now *= now;
    k /= 2;
  }
  return ret;
}
long long beki(long long n, long long k, long long md) {
  long long ret = 1;
  long long now = n;
  now %= md;
  while (k > 0) {
    if (k % 2 == 1) {
      ret *= now;
      ret %= md;
    }
    now *= now;
    now %= md;
    k /= 2;
  }
  return ret;
}
long long gyaku(long long n, long long md) { return beki(n, md - 2, md); }
long long poc(long long n) {
  long long ret = 0;
  long long u = n;
  while (u > 0) {
    ret += u % 2;
    u /= 2;
  }
  return ret;
}
struct UF {
 private:
  vector<long long> par, len, you;

 public:
  UF(long long n) {
    for (int i = 0; i < n; i++) {
      par.push_back(i);
      len.push_back(0);
      you.push_back(1);
    }
  }
  long long root(long long n) {
    if (par[n] == n)
      return n;
    else
      return par[n] = root(par[n]);
  }
  void unit(long long a, long long b) {
    a = root(a);
    b = root(b);
    if (a == b) return;
    if (len[a] < len[b]) {
      par[a] = b;
      you[b] += you[a];
    } else {
      par[b] = a;
      you[a] += you[b];
      if (len[a] == len[b]) len[a]++;
    }
  }
  long long yo(long long a) {
    a = root(a);
    return you[a];
  }
};
struct ST {
 private:
  long long n;
  vector<pair<long long, long long> > dat;

 public:
  ST(vector<long long> v) {
    long long sz = v.size();
    n = 1;
    while (n < sz) n *= 2;
    pair<long long, long long> p = {inf, inf};
    dat.resize(2 * n - 1, p);
    for (int i = 0; i < sz; i++) dat[i + n - 1] = {v[i], i};
    for (long long i = n - 2; i >= 0; i--) {
      dat[i] = min(dat[i * 2 + 1], dat[i * 2 + 2]);
    }
  }
  void add(long long k, long long x) {
    long long i = k + n - 1;
    dat[i] = {x, k};
    while (i > 0) {
      i = (i - 1) / 2;
      dat[i] = min(dat[2 * i + 1], dat[2 * i + 2]);
    }
  }
  pair<long long, long long> que(long long a, long long b, long long k = 0,
                                 long long l = 0, long long r = -1) {
    if (r < 0) r = n;
    if (b <= l || a >= r) return {inf, inf};
    if (a <= l && b >= r) return dat[k];
    pair<long long, long long> m1 = que(a, b, 2 * k + 1, l, (l + r) / 2);
    pair<long long, long long> m2 = que(a, b, 2 * k + 2, (l + r) / 2, r);
    return min(m1, m2);
  }
  long long get(long long k) { return dat[k + n - 1].first; }
};
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  long long n, d;
  cin >> n >> d;
  vector<long long> ti(n), oo(n);
  for (int i = 0; i < n; i++) {
    long long a;
    cin >> a;
    ti[i] = a - i * d;
    oo[i] = a + i * d;
  }
  ST seg1(ti), seg2(oo);
  UF uf(n);
  long long ans = 0;
  multiset<long long> st[n];
  int cnt = 0;
  for (;;) {
    vector<pair<long long, pair<long long, long long> > > v;
    for (int i = 0; i < n; i++) {
      long long pa = uf.root(i);
      if (pa != i) continue;
      pair<long long, long long> p1 = seg2.que(i + 1, n);
      pair<long long, long long> p2 = seg1.que(0, i);
      long long co1 = ti[i] + p1.first;
      long long co2 = oo[i] + p2.first;
      v.push_back({co2, {i, p2.second}});
      v.push_back({co1, {i, p1.second}});
    }
    sort(v.begin(), v.end());
    for (int i = 0; i < v.size(); i++) {
      long long co = v[i].first, f = v[i].second.first, t = v[i].second.second;
      if (uf.root(f) == uf.root(t)) continue;
      cnt++;
      ans += co;
      uf.unit(f, t);
      long long pa = uf.root(f);
      long long e = seg1.get(f), ee = seg1.get(t);
      seg1.add(pa, min(e, ee));
      e = seg2.get(f);
      ee = seg2.get(t);
      seg2.add(pa, min(e, ee));
    }
    if (cnt == n - 1) break;
    for (int i = 0; i < n; i++) {
      long long pa = uf.root(i);
      if (pa != i) {
        seg1.add(i, inf);
        seg2.add(i, inf);
      }
    }
  }
  cout << ans << endl;
}
