#include <iostream>
#include <cstdio>
#include <string>
#include <cstring>
#include <deque>
#include <list>
#include <queue>
#include <stack>
#include <vector>
#include <utility>
#include <algorithm>
#include <map>
#include <set>
#include <complex>
#include <cmath>
#include <limits>
#include <climits>
#include <ctime>
#include <cassert>
#include <numeric>
#include <functional>
#include <bitset>

using namespace std;
using lint = long long int;
long long int INF = 1001001001001001LL;
int inf = 1000000007;
long long int MOD = 1000000007LL;
double PI = 3.1415926535897932;

template<typename T1,typename T2>inline void chmin(T1 &a,const T2 &b){if(a>b) a=b;}
template<typename T1,typename T2>inline void chmax(T1 &a,const T2 &b){if(a<b) a=b;}

#define ALL(a) a.begin(),a.end()
#define RALL(a) a.rbegin(),a.rend()

/* do your best */

// quoted from beet-aizu
template <typename T, typename E, typename F, typename G>
struct SegmentTree{
    // using F = function<T(T, T)>
    // using G = function<T(T, E)>
    int n;
    F f;
    G g;
    T ti;
    vector<T> dat;
    SegmentTree(){};
    SegmentTree(F f,G g,T ti):f(f),g(g),ti(ti){}
    void init(int n_){    
        n=1;
        while(n<n_) n<<=1;
        dat.assign(n<<1,ti);
    }
    void build(const vector<T> &v){
        int n_=v.size();
        init(n_);
        for(int i=0;i<n_;i++) dat[n+i]=v[i];
        for(int i=n-1;i;i--)
            dat[i]=f(dat[(i<<1)|0],dat[(i<<1)|1]);
    }
    void update(int k,const E &x){
        k += n;
        dat[k] = g(dat[k], x);
        while(k>>=1)
            dat[k]=f(dat[(k<<1)|0],dat[(k<<1)|1]);    
    }
    T operator [](int k) const { return dat[k+n]; }
    T query(int a,int b) const {
        T vl=ti,vr=ti;
        for(int l=a+n,r=b+n;l<r;l>>=1,r>>=1) {
            if(l&1) vl=f(vl,dat[l++]);
            if(r&1) vr=f(dat[--r],vr);
        }
        return f(vl,vr);
    }

    /* TODO わからない 聞く 
    template<typename C>
    int find(int a,int b,C &check,int k,int l,int r){
        if(!check(dat[k])||r<=a||b<=l) return -1;
        if(k>=n) return k-n;
        int m=(l+r)>>1;
        int vl=find(a,b,check,(k<<1)|0,l,m);
        if(~vl) return vl;
        return find(a,b,check,(k<<1)|1,m,r);
    }
    template<typename C>
    int find(int a,int b,C &check){
        return find(a,b,check,1,0,n);
    }*/
    
};

// 最小全域技を求める
// O(E log V)
// verify http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=GRL_2_A

template<typename T>
T prim(vector<vector<pair<int, T>>> &g){
    int n = (int)g.size();
    T ret = 0;
    vector<bool> used(n, false);
    using P = pair<T, int>;
    priority_queue<P, vector<P>, greater<P>> que;
    que.push({0, 0});
    while(!que.empty()){
        auto p = que.top();
        que.pop();
        if(used[p.second]) continue;
        used[p.second] = true;
        ret += p.first;
        for(auto &e : g[p.second]){
            que.push({e.second, e.first});
        }
    }

    return ret;
}

int main(){
  using T = pair<lint, lint>;  // type T
  using E = lint;  // type E
  auto f = [](T a, T b){ // return type T value
    return min(a, b);
  };
  auto g = [](T a, E b){ // return type T value
    return make_pair(b, a.second);  // return b;
  };
  T ti = {INF, -1};  // identify element
  lint n, D; cin >> n >> D;
  vector<pair<lint, lint>> dat(n);
  for(int i = 0; i < n; i++) {
    dat[i] = {INF, i};
  }
  SegmentTree<T, E, decltype(f), decltype(g)> sg1(f, g, ti);  // don't change
  sg1.build(dat);   // 初期配列を代入
  SegmentTree<T, E, decltype(f), decltype(g)> sg2(f, g, ti);  // don't change
  sg2.build(dat);   // 初期配列を代入
  
  vector<vector<pair<int, lint>>> graph(n);

  vector<lint> a(n);
  for(int i = 0; i < n; i++) cin >> a[i];
  for(int i = 0; i < n; i++) {
    sg1.update(i, -i * D + a[i]);
    sg2.update(i,  i * D + a[i]);
  }
  
  // cout << sg1.query(0, n).first << " " << sg1.query(0, n).second << endl;

  vector<pair<lint, lint>> pv(n);
  for(int i = 0; i < n; i++) pv[i] = {a[i], i};
  sort(RALL(pv));

  for(int i = 0; i < n; i++) {
    lint id = pv[i].second;
    lint id1 = sg1.query(0, id).second;
    lint id2 = sg2.query(id + 1, n).second;
    // cerr << id << " " << id1 << " " << id2 << endl;
    if(id1 != -1) {
      graph[id].push_back({id1, a[id] + a[id1] + (int)abs(id - id1) * D});
      graph[id1].push_back({id, a[id] + a[id1] + (int)abs(id - id1) * D});
    }
    if(id2 != -1) {
      graph[id].push_back({id2, a[id] + a[id2] + (int)abs(id - id2) * D});
      graph[id2].push_back({id, a[id] + a[id2] + (int)abs(id - id2) * D});
    }
    
    sg1.update(id, INF);
    sg2.update(id, INF);
    // sg1.update(id1, INF);
    // sg2.update(id2, INF);
  }
  
  cout << prim(graph) << endl;

  return 0;
}


Measured memory_bytes: 60140