#include <bits/stdc++.h>
using namespace std;
const int inf = 0x3f3f3f3f;
const long long inf2 = 0x3f3f3f3f3f3f3f3f;
const double eps = 1e-6;
const int mod = 1000000007;
namespace fastio {
char in[100000];
int itr = 0, llen = 0;
char get() {
  if (itr == llen) llen = fread(in, 1, 100000, stdin), itr = 0;
  if (llen == 0) return EOF;
  return in[itr++];
}
char out[100000];
int itr2 = 0;
void put(char c) {
  out[itr2++] = c;
  if (itr2 == 100000) {
    fwrite(out, 1, 100000, stdout);
    itr2 = 0;
  }
}
int clear() {
  fwrite(out, 1, itr2, stdout);
  itr2 = 0;
  return 0;
}
int getint() {
  int r = 0;
  bool ng = 0;
  char c;
  c = get();
  while (c != '-' && (c < '0' || c > '9')) c = get();
  if (c == '-') ng = 1, c = get();
  while (c >= '0' && c <= '9') r = r * 10 + c - '0', c = get();
  return ng ? -r : r;
}
string getstr() {
  string ret = "";
  char ch = get();
  while (ch == ' ' || ch == '\n') ch = get();
  while (ch != ' ' && ch != '\n') ret.push_back(ch), ch = get();
  return ret;
}
void putstr(string s) {
  for (int i = 0; i < s.size(); i++) put(s[i]);
}
void putint(int x) {
  if (x < 0) {
    put('-');
    x = -x;
  }
  if (x == 0) {
    put('0');
    return;
  }
  char c[20];
  int pos = 0;
  while (x) {
    c[pos++] = '0' + x % 10;
    x /= 10;
  }
  for (int i = pos - 1; i >= 0; i--) put(c[i]);
}
void getarr(int arrname[], int size) {
  for (int i = 0; i < size; i++) arrname[i] = getint();
}
}  // namespace fastio
using namespace fastio;
int n, d;
int a[200005];
int dpl[200005], dpr[200005];
long long ans = 0;
int main() {
  n = getint();
  d = getint();
  for (int i = 0; i < n; i++) a[i] = getint(), ans += a[i];
  ans += (n - 1) * d;
  dpl[0] = a[0];
  for (int i = 1; i < n; i++) dpl[i] = min(dpl[i - 1] + d, a[i]);
  dpr[n - 1] = a[n - 1];
  for (int i = n - 2; i >= 0; i--) dpr[i] = min(dpr[i + 1] + d, a[i]);
  for (int i = 1; i < n - 1; i++) ans += min(dpl[i], dpr[i]);
  cout << ans << endl;
  return 0;
}
