#include <bits/stdc++.h>
#include <map>
#include <set>
#include <vector>
#include <algorithm>
#include <iostream>
#include <bitset>
#include <cassert>
#include <queue>
#include <random>
#include <stack>
#include <iomanip>
#include <math.h>
using namespace std;
#define rep(i, n) for (ll i = 0; i < (ll)n; i++)
#define repf(i, a, b) for (ll i = (ll)a; i < (ll)b; i++)
#define repr(i, a, b) for (ll i = (ll)a; i > (ll)b; i--)
#define repv(x, arr) for (auto &x : arr)
#define all(v) (v).begin(), (v).end()
#define vec(name, num) vector<ll> name((num), 0);
#define mp(a, b) make_pair(a, b)
#define pb(x) push_back(x)
#define F first
#define S second
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ld, ld> pdd;
typedef vector<ll> vll;
typedef vector<vll> vvll;
typedef vector<int> vii;
typedef vector<vii> vvii;
const ll mod = 1e9 + 7;
const int infi = 2147483600;
const ll infl = 1e17;

struct SegmentTree
{
private:
    int N;
    vector<ll> node;
    ll e;

public:
    SegmentTree() {}
    SegmentTree(ll e) : e(e) {}
    void __init__(int sz)
    {
        N = 1;
        while (N < sz)
            N *= 2;
        node.resize(2 * N - 1, e);
    }
    void build(vector<ll> &v)
    {
        int sz = (int)(v.size());
        __init__(sz);
        rep(i, sz)
        {
            node[i + N - 1] = v[i];
        }
        for (int i = N - 2; i >= 0; i--)
        {
            node[i] = min(node[i * 2 + 1], node[i * 2 + 2]);
        }
    }
    void update(int k, ll x)
    {
        k += N - 1;
        node[k] = x;
        while (k > 0)
        {
            k = (k - 1) / 2;
            node[k] = min(node[2 * k + 1], node[2 * k + 2]);
        }
        return;
    }
    ll query(int a, int b) { return query(a, b, 0, 0, N); }
    ll query(int a, int b, int k, int l, int r)
    {
        if (b <= l || r <= a)
            return e;
        if (a <= l && r <= b)
            return node[k];
        ll vl, vr;
        vl = query(a, b, 2 * k + 1, l, (l + r) / 2);
        vr = query(a, b, 2 * k + 2, (l + r) / 2, r);
        return min(vl, vr);
    }
    ll show_one(int i)
    {
        if (0<=i && i<N)
            return node[i + N - 1];
        return e;
    }

    int need()
    {
        int k = 0;
        while (k < N - 1)
        {
            node[k] = min(node[2 * k + 1], node[2 * k + 2]);
            if (node[k] == node[2 * k + 1])
            {
                k = 2 * k + 1;
            }
            else if (node[k] == node[2 * k + 2])
            {
                k = 2 * k + 2;
            }
        }
        return k - N + 1;
    }
    void view(){
        repf(k, N - 1, 2 * N - 1){
            if (node[k]==e)
                cout << "inf ";
            else cout << node[k] << " ";}
        cout << endl;
        return;
    }
};

struct UnionFind
{
    vector<int> root;
    int n;
    void __init__(int sz)
    {
        n = sz;
        root.resize(n, -1);
    }
    int find(int x)
    {
        if (root[x] >= 0)
        {
            root[x] = find(root[x]);
            return root[x];
        }
        return x;
    }
    void unit(int a, int b)
    {
        int ra, rb;
        ra = find(a);
        rb = find(b);
        if (ra == rb)
        {
            return;
        }
        else if (root[ra] <= root[rb])
        {
            root[ra] += root[rb];
            root[rb] = ra;
        }
        else
        {
            root[rb] += root[ra];
            root[ra] = rb;
        }
        return;
    }
    int count()
    {
        set<int> cnt;
        rep(i, n)
            cnt.insert(find(i));
        return cnt.size();
    }
};

int main()
{
    ll n,d;
    cin >> n >> d;
    vll a(n);
    rep(i, n) cin >> a[i];
    SegmentTree seg(infl);
    seg.build(a);
    ll ans = 0;
    ll cnt = n - 1;
    vvll idx(n, vll(2));
    rep(i,n){
        idx[i][0] = i;
        idx[i][1] = i;
    }
    while (cnt>0){
        /*cout << ans;
        cout << endl;
        seg.view(); */
        int k = seg.need();
        ll x = seg.show_one(k);
        //cout << k << " " << x << " ";
        if (k>0 && seg.show_one(k - 1) < infl)
        {
            ans += seg.show_one(k - 1) + x + d;
            
            seg.update(idx[k-1][0], min(x + (k - idx[k-1][0]) * d, seg.show_one(idx[k-1][0])));
            if (idx[k-1][0]<k-1){
                seg.update(k - 1, infl);
            }
            idx[idx[k][1]][0] = idx[k - 1][0];
            idx[k][0] = idx[k - 1][0];
            idx[k - 1][1] = idx[k][1];
            idx[idx[k - 1][0]][1] = idx[k][1];
            cnt--;
        }
        if (k<n && seg.show_one(k + 1) < infl)
        {
            ans += seg.show_one(k + 1) + x + d;
            seg.update(idx[k+1][1], min(x + (idx[k+1][1] - k) * d, seg.show_one(idx[k+1][1])));
            if (idx[k+1][1]>k+1){
                seg.update(k + 1, infl);
            }
            idx[idx[k][0]][1] = idx[k + 1][1];
            idx[k][1] = idx[k + 1][1];
            idx[idx[k + 1][1]][0] = idx[k][0];
            idx[k + 1][0] = idx[k][0];
            cnt--;

        }
        seg.update(k, infl);
    }
    //rep(i, n) cout << seg.show_one(i) << " ";
    //cout << endl;
    cout << ans << endl;
    //seg.view();
}


Measured memory_bytes: 16896