#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 int MOD = 1000000007;

template <typename T, typename E>
struct lazySegTree {
  using F = function<T(T,T)>;
  using G = function<T(T,E)>;
  using H = function<E(E,E)>;
  using P = function<E(E,int)>;
  F f; G g; H h; P p; T d1; E d0;
  int n;
  vector<T> dat;
  vector<E> lazy;

  lazySegTree(){}
  lazySegTree(int n_, F f_, G g_, H h_, 
    T d1_, E d0_, P p_=[](E a, int b){return a;})
    : f(f_), g(g_), h(h_), p(p_), d1(d1_), d0(d0_) 
  {
    n = 1; while(n < n_) n *= 2;
    dat.assign(n*2-1, d1);
    lazy.assign(n*2-1, d0);
  }
  void build(vector<T> v) {
    REP(i, v.size()) dat[i+n-1] = v[i];
    for(int i=n-2; i>=0; --i) dat[i] = f(dat[i*2+1], dat[i*2+2]);
  }

  // 区間の幅がlenの節点kについて遅延評価
  inline void eval(int len, int k) {
    if(lazy[k] == d0) return;
    if(k*2+1 < n*2-1) {
      lazy[2*k+1] = h(lazy[k*2+1], lazy[k]);
      lazy[2*k+2] = h(lazy[k*2+2], lazy[k]);
    }
    dat[k] = g(dat[k],p(lazy[k],len));
    lazy[k] = d0;
  }
  // [a, b)
  T update(int a, int b, E x, int k, int l, int r) {
    eval(r-l, k);
    if(b <= l || r <= a) return dat[k];
    if(a <= l && r <= b) {
      lazy[k] = h(lazy[k], x);
      return g(dat[k], p(lazy[k],r-l));
    }
    return dat[k] = f(update(a, b, x, 2*k+1, l, (l+r)/2),
                      update(a, b, x, 2*k+2, (l+r)/2, r));
  }
  T update(int a, int b, E x) { return update(a, b, x, 0, 0, n); }
  // [a, b)
  T query(int a, int b, int k, int l, int r) {
    eval(r-l, k);
    if(a <= l && r <= b) return dat[k];
    bool left = !((l+r)/2 <= a || b <= l), right = !(r <= 1 || b <= (l+r)/2);
    if(left&&right) return f(query(a, b, 2*k+1, l, (l+r)/2), query(a, b, 2*k+2, (l+r)/2, r));
    if(left) return query(a, b, 2*k+1, l, (l+r)/2);
    return query(a, b, 2*k+2, (l+r)/2, r);
  }
  T query(int a, int b) { return query(a, b, 0, 0, n); }
  // デバッグ出力
  void debug() {
    cout << "---------------------" << endl;
    int cnt = 0;
    for(int i=1; i<=n; i*=2) {
      REP(j, i) {
        cout << "(" << dat[cnt] << "," << lazy[cnt] << ") "; 
        cnt++;
      }
      cout << endl;
    }
    cout << "---------------------" << endl;
  }
};
/**
* 区間更新区間max d1=d0=INT_MAX f=max(a,b) g=h=(b==INT_MAX?a:b)\n
* 区間加算区間和  d1=d0=0 f=g=h=a+b p=a*b\n
* 区間加算区間min d1=d0=0 f=min(a,b) g=h=a+b\n
* 区間更新区間和  d1=d0=0 f=a+b g=h=(b==0?a:b) p=a*b\n
* 区間xor区間和   d1=d0=0 f=a+b g=(b>=1?b-a:a) h=a^b p=a*b
*/

struct UnionFind {
  vector<int> par, s;
  UnionFind(int n=2e5) { init(n); }
  void init(int n) { 
    s.assign(n, 1); par.resize(n); 
    iota(par.begin(), par.end(), 0);
  }
  int find(int x) {
    if(par[x] == x) return x;
    return par[x] = find(par[x]);
  }
  void unite(int x, int y) {
    x = find(x);
    y = find(y);
    if(x == y) return;
    if(s[x] < s[y]) par[x] = y, s[y] = s[x] + s[y];
    else par[y] = x, s[x] = s[x] + s[y];
  }
  bool same(int x, int y) { return find(x) == find(y); }
  int size(int x) { return s[find(x)]; }
};

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

  ll n, d;
  cin >> n >> d;
  vector<PII> a(n);
  REP(i, n) cin >> a[i].first, a[i].second = i;

  auto f = [](PII a, PII b) { return min(a, b); };
  auto g = [](PII a, PII b) { return PII{a.first+b.first, a.second}; };
  vector<ll> x, y, z;
  // iより左の頂点とつなぐ
  lazySegTree<PII,PII> seg(n, f, g, g, PII{0,0}, PII{0,0});
  seg.build(a);
  FOR(i, 1, n) {
    seg.update(0, i, PII{d,0});
    auto p = seg.query(0, i);
    ll cost = p.first + a[i].first, idx = p.second;
    x.push_back(i), y.push_back(idx), z.push_back(cost);
  }
  // iより右の頂点とつなぐ
  lazySegTree<PII,PII> seg2(n, f, g, g, PII{0,0}, PII{0,0});
  seg2.build(a);
  for(ll i=n-2; i>=0; --i) {
    seg2.update(i+1, n, PII{d,0});
    auto p = seg2.query(i+1, n);
    ll cost = p.first + a[i].first, idx = p.second;
    x.push_back(i), y.push_back(idx), z.push_back(cost);
  }
  // Kruskal
  ll m = x.size(), ret = 0;
  UnionFind uf(n);
  vector<ll> idx(m);
  iota(ALL(idx), 0);
  sort(ALL(idx), [&](ll l, ll r){
    return z[l] < z[r];
  });
  REP(i, m) {
    if(uf.same(x[idx[i]], y[idx[i]])) continue;
    uf.unite(x[idx[i]], y[idx[i]]);
    ret += z[idx[i]];
  }
  cout << ret << endl;
}
