#include <bits/stdc++.h>
using namespace std;
struct InputReader {
  char buf[1000001];
  int p;
  inline InputReader() { p = 1000001; }
  inline void Flush() {
    p = 0;
    fread(buf, 1, 1000001, stdin);
  }
  inline char C() {
    if (p >= 1000001) Flush();
    return buf[p++];
  }
  inline char Readnum() {
    char ch = C();
    while (!isdigit(ch) && ch != '-') ch = C();
    return ch;
  }
  inline void Readalpha(char &c) {
    c = C();
    while (!isalpha(c)) c = C();
  }
  int operator()() {
    int ans = 0, fu = 1;
    char ch = Readnum();
    if (ch == '-') fu = -1, ch = C();
    while (ch >= '0' && ch <= '9') {
      ans = ans * 10 + ch - '0';
      ch = C();
    }
    return ans * fu;
  }
  long long Readll() {
    long long ans = 0LL, fu = 1LL;
    char ch = Readnum();
    if (ch == '-') fu = -1LL, ch = C();
    while (ch >= '0' && ch <= '9') {
      ans = ans * 10LL + ch - '0';
      ch = C();
    }
    return ans * fu;
  }
  inline void Readstring(string &x) {
    x.clear();
    char ch = C();
    while (!isdigit(ch) && !isalpha(ch) && ch != '#' && ch != '.') ch = C();
    while (isdigit(ch) || isalpha(ch) || ch == '#' || ch == '.') {
      x += ch;
      ch = C();
    }
  }
  inline void Readchstring(char s[]) {
    int len = 0;
    char ch = C();
    while (!isdigit(ch) && !isalpha(ch)) ch = C();
    while (isdigit(ch) || isalpha(ch)) {
      s[len++] = ch;
      ch = C();
    }
    s[len] = '\0';
  }
  inline void Specialread(char &c) {
    c = C();
    while (!isdigit(c) && !isalpha(c) && c != '#' && c != '.' && c != '=' &&
           c != 'B')
      c = C();
  }
} In;
inline void Read(int &x) { x = In(); }
inline void Read(int &x, int &y) {
  x = In();
  y = In();
}
inline void Read(int &x1, int &x2, int &x3) {
  x1 = In();
  x2 = In();
  x3 = In();
}
inline void Read(int &x1, int &x2, int &x3, int &x4) {
  x1 = In();
  x2 = In();
  x3 = In();
  x4 = In();
}
inline void Read(long long &x) { x = In.Readll(); }
inline void Read(long long &x, long long &y) {
  x = In.Readll();
  y = In.Readll();
}
inline void Read(long long &x1, long long &x2, long long &x3) {
  x1 = In.Readll();
  x2 = In.Readll();
  x3 = In.Readll();
}
inline void Read(long long &x1, long long &x2, long long &x3, long long &x4) {
  x1 = In.Readll();
  x2 = In.Readll();
  x3 = In.Readll();
  x4 = In.Readll();
}
template <typename T>
inline void Read(T a[], int s, int t) {
  for (int(i) = (s); (i) <= (t); ++(i)) Read(a[i]);
}
inline void FILEIO() {}
inline void FILEIO(string pname) {
  freopen((pname + ".in").c_str(), "r", stdin);
  freopen((pname + ".out").c_str(), "w", stdout);
}
void Printtime() {}
void END() {
  Printtime();
  exit(0);
}
template <typename T>
void END(T mes) {
  cout << mes << endl;
  END();
}
template <typename T>
void Print(T a[], int s, int t, char sp = ' ', char ed = '\n') {
  if (s > t) return;
  for (int i = s; i < t; i++) cout << a[i] << sp;
  cout << a[t] << ed;
  cout.flush();
}
template <typename T>
void Print(T a, int s = 0, int t = -1, char sp = ' ', char ed = '\n') {
  if (t == -1) t = a.size() - 1;
  for (int i = s; i <= t; i++) cout << a[i] << sp;
  cout << ed;
  cout.flush();
}
struct E {
  int f, t;
  long long c;
};
int n;
long long a[262144], d;
vector<E> es;
long long f[262144], g[262144];
void Divideandconquer(int l, int r) {
  if (l == r) return;
  int mid = l + r >> 1;
  Divideandconquer(l, mid);
  Divideandconquer(mid + 1, r);
  int minf = *min_element(f + l, f + mid + 1);
  int minfpos;
  for (int(i) = (l); (i) <= (mid); ++(i)) minfpos = f[i] == minf ? i : minfpos;
  int ming = *min_element(g + mid + 1, g + r + 1);
  int mingpos;
  for (int(i) = (mid + 1); (i) <= (r); ++(i))
    mingpos = g[i] == ming ? i : mingpos;
  for (int(i) = (mid + 1); (i) <= (r); ++(i))
    es.push_back({minfpos, i, minf + g[i]});
  for (int(i) = (l); (i) <= (mid); ++(i))
    es.push_back({i, mingpos, f[i] + ming});
}
int dsu[262144];
void Init() {
  for (int(i) = 1; (i) <= (n); ++(i)) dsu[i] = i;
}
int Findfa(int pos) {
  return dsu[pos] == pos ? pos : dsu[pos] = Findfa(dsu[pos]);
}
bool Unite(int a, int b) {
  a = Findfa(a);
  b = Findfa(b);
  if (a == b) return 0;
  dsu[a] = b;
  return 1;
}
long long Kruskal() {
  Init();
  long long ans = 0;
  for (auto ue : es) {
    if (Unite(ue.f, ue.t)) ans += ue.c;
  }
  return ans;
}
int main() {
  FILEIO();
  Read(n);
  Read(d);
  for (int(i) = 1; (i) <= (n); ++(i)) Read(a[i]);
  for (int(i) = 1; (i) <= (n); ++(i)) {
    f[i] = a[i] - i * d;
    g[i] = a[i] + i * d;
  }
  Divideandconquer(1, n);
  sort(es.begin(), es.end(), [](const E &a, const E &b) { return a.c < b.c; });
  long long ans = Kruskal();
  cout << ans << endl;
  END();
}
