#include <bits/stdc++.h>

using namespace std;
using ll = long long;
// #define int ll
using PII = pair<ll, ll>;

#define FOR(i, a, n) for (ll i = (ll)a; i < (ll)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()

template<typename T> T &chmin(T &a, const T &b) { return a = min(a, b); }
template<typename T> T &chmax(T &a, const T &b) { return a = max(a, b); }
template<typename T> bool IN(T a, T b, T x) { return a<=x&&x<b; }
template<typename T> T ceil(T a, T b) { return a/b + !!(a%b); }

template<typename T> vector<T> make_v(size_t a) { return vector<T>(a); }
template<typename T,typename... Ts>
auto make_v(size_t a,Ts... ts) {
  return vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));
}
template<typename T,typename V> typename enable_if<is_class<T>::value==0>::type
fill_v(T &t, const V &v) { t=v; }
template<typename T,typename V> typename enable_if<is_class<T>::value!=0>::type
fill_v(T &t, const V &v ) { for(auto &e:t) fill_v(e,v); }

template<class S,class T>
ostream &operator <<(ostream& out,const pair<S,T>& a){
  out<<'('<<a.first<<','<<a.second<<')'; return out;
}
template<typename T>
istream& operator >> (istream& is, vector<T>& vec){
  for(T& x: vec) {is >> x;} return is;
}
template<class T>
ostream &operator <<(ostream& out,const vector<T>& a){
  out<<'['; for(T i: a) {out<<i<<',';} out<<']'; return out;
}

int dx[] = {0, 1, 0, -1}, dy[] = {1, 0, -1, 0}; // DRUL
const int INF = 1<<30;
const ll LLINF = 1LL<<60;
const ll MOD = 1000000007;

signed main(void) 
{
  cin.tie(0);
  ios::sync_with_stdio(false);

  ll n, d;
  cin >> n >> d;
  vector<ll> a(n);
  REP(i, n) cin >> a[i];

  vector<bool> flag1(n);
  vector<ll> b(n), pfxb(n);
  REP(i, n) b[i] = a[i]-i*d;
  pfxb[0] = LLINF;
  REP(i, n) {
    if(b[i] < pfxb[i]) {
      flag1[i] = 1;
      pfxb[i+1] = b[i];
    } else {
      pfxb[i+1] = pfxb[i];
    }
  }

  vector<bool> flag2(n);
  vector<ll> c(n), sfxc(n+1);
  REP(i, n) c[i] = a[i]+i*d;
  sfxc[n] = LLINF;
  for(ll i=n-1; i>=0; --i) {
    if(c[i] < sfxc[i+1]) {
      flag2[i] = 1;
      sfxc[i] = c[i];
    } else {
      sfxc[i] = sfxc[i+1];
    }
  }

  ll prev = -1, ret = 0;
  REP(i, n) {
    if(flag1[i] && flag2[i]) {
      if(prev != -1) {
        ret += a[i] + a[prev] + d * (i-prev);
      }
      prev = i;
    } else {
      ll t1 = pfxb[i] + a[i] + i*d;
      ll t2 = sfxc[i] + a[i] - i*d;
      ret += min(t1, t2);
    }
  }
  cout << ret << endl;

  return 0;
}