#include <algorithm>
#include <cassert>
#include <cfloat>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <deque>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <vector>

#define FOR(i,k,n) for(int(i)=(k);(i)<(n);++(i))
#define rep(i,n) FOR(i,0,n)
#define all(v) begin(v),end(v)
#define debug(x) std::cerr<<#x<<": "<<x<<"\n"
#define debug2(x,y) std::cerr<<#x<<": "<<x<<", "<<#y<<": "<<y<<"\n"
#define debug3(x,y,z) std::cerr<<#x<<": "<<x<<", "<<#y<<": "<<y<<", "<<#z<<": "<<z<<"\n"

typedef long long ll;
typedef std::vector<int> vi;
typedef std::vector<vi> vvi;
typedef std::vector<ll> vll;
typedef std::vector<vll> vvll;
template<typename T> using vvec=std::vector<std::vector<T>>;
template<typename T>
auto make_v(size_t sz){return std::vector<T>(sz);}
template<typename T,typename... Ts>
auto make_v(size_t sz,Ts...ts){return std::vector<decltype(make_v<T>(ts...))>(sz,make_v<T>(ts...));}
template<typename T>
void fill_v(T&var,const T&x){var=x;}
template<typename V,typename T>
void fill_v(V&v,const T&x){for(auto&& w:v){fill_v(w,x);}}

template<typename T> std::ostream& operator<<(std::ostream&s,const std::vector<T>&v){
  int sz=v.size();s<<"\n";rep(i,sz){s<<v[i];if(i<sz-1){s<<"\t";}}s<<"\n";return s;}
template<typename T> std::ostream& operator<<(std::ostream&s,const std::vector<std::vector<T>>&v){
  for(auto&& w:v){s<<w;}return s;}
template<typename T> std::ostream& operator<<(std::ostream&s,const std::deque<T>&v){
  int sz=v.size();s<<"\n";rep(i,sz){s<<v[i];if(i<sz-1){s<<"\t";}}s<<"\n";return s;}
template<typename T> std::ostream& operator<<(std::ostream&s,const std::deque<std::deque<T>>&v){
  for(auto&& w:v){s<<w;}return s;}
template<typename T> std::ostream& operator<<(std::ostream&s, const std::set<T>&v){
  s<<"\n";for(auto&& elm:v){s<<elm<<"\t";}s<<"\n";return s;}

inline void scan(int&a){scanf("%d",&a);}
inline void scan(ll&a){scanf("%lld",&a);}
inline void scan(char&a){scanf(" %c",&a);}
inline void scan(double&a){scanf("%lf",&a);}
template<typename T>
inline void scan(std::vector<T>&v){int sz=v.size();rep(i,sz){scan(v[i]);}}
template<typename First,typename...Args>
inline void scan(First&f,Args&...args){scan(f);scan(args...);}
inline void scan(std::string&s){char BUF[3000000];scanf(" %s",BUF);s=std::string(BUF);}
inline void print(int a){printf("%d\n",a);}
inline void print(ll a){printf("%lld\n",a);}
inline void print(double a){printf("%.12f\n",a);}
inline void print(std::string s){std::cout<<s<<"\n";}

using namespace std;

struct edge {
  int to;
  ll cost;
};

struct info {
  int origin;
  ll cost;
};

int main() {
  int n;
  scan(n);
  ll d;
  scan(d);
  vll a(n);
  scan(a);
  ll INF = LLONG_MAX / 2;
  auto g = make_v<edge>(2*n, 0);
  rep (i, n) {
    g[i].push_back({i+n, a[i]});
    g[i+n].push_back({i, a[i]});
  }
  rep (i, n-1) {
    g[i+n].push_back({i+1+n, d});
    g[i+1+n].push_back({i+n, d});
  }
  auto infos = vector<info>(2*n);
  rep (i, n) {
    infos[i] = {i, 0};
    infos[i+n] = {-1, INF};
  }

  vvll edges;
  priority_queue<vll, vvll, greater<vll>> q;
  vector<bool> fixed(2*n, false);
  rep (i, n) {
    q.push({0LL, (ll)i});
  }

  while (!q.empty()) {
    ll curr_cost = q.top()[0];
    int u = q.top()[1];
    q.pop();
    if (fixed[u]) { continue; }
    fixed[u] = true;
    for (auto&& e : g[u]) {
      int v = e.to;
      if (fixed[v]) {
        if (infos[u].origin != infos[v].origin) {
          edges.push_back({curr_cost + e.cost + infos[v].cost, infos[u].origin, infos[v].origin});
        }
        continue;
      }
      ll new_cost = curr_cost + e.cost;
      if (infos[v].cost > new_cost) {
        infos[v].cost = new_cost;
        infos[v].origin = infos[u].origin;
        q.push({new_cost, v});
      }
    }
  }
  //debug(edges.size());
  //debug(edges);
  assert((int)edges.size() == n-1);
  ll ans = 0;
  for (auto&& e : edges) {
    ans += e[0];
  }
  print(ans);

  return 0;
}


Measured memory_bytes: 64492