using System;
using System.Collections.Generic;
using System.Linq;
using static System.Console;
using static System.Convert;
using static System.Math;
//using Debug;
//using static System.Globalization.CultureInfo;
using System.Text;
class Program
{
    static void Main(string[] args)
    {
        Solve();
        //WriteLine(Solve());
    }
    static int[] ar;
    static void Solve()
    {
        var nd = Pair<int,long>.makePair();
        ar = Input.ar;
        var so = Enumerable.Range(0, nd.v1).Select(v => new Pair<int, int>(ar[v], v)).OrderBy(v=>v).ToArray();
        var edge = new List<Pair<long, int, int>>();
        Func<Pair<long, int>, Pair<long, int>, Pair<long, int>> func =
            (a, b) => a.v1 > b.v1 ? b : a;
        var leftseg = new SegmentTree<Pair<long,int>>(nd.v1, new Pair<long, int>(long.MaxValue,-1), func);
        var rightseg = new SegmentTree<Pair<long,int>>(nd.v1, new Pair<long, int>(long.MaxValue,-1), func);
        for(var i = 0; i < nd.v1; i++)
        {
            leftseg.Update(i, new Pair<long, int>(ar[i] - i * nd.v2,i));
            rightseg.Update(i, new Pair<long, int>(ar[i] + i * nd.v2,i));
        }
        for(var i = nd.v1-1; i >= 0; i--)
        {
            if (so[i].v2 != 0)
            {
                var min = leftseg.Query(0, so[i].v2);
                edge.Add(new Pair<long, int, int>(min.v1 + so[i].v2 * nd.v2 + so[i].v1, so[i].v2, min.v2));
                leftseg.Update(so[i].v2, new Pair<long, int>(long.MaxValue,-1));
            }
            if (so[i].v2 != nd.v1 - 1)
            {
                var min = rightseg.Query(so[i].v2 + 1, nd.v1);
                edge.Add(new Pair<long, int, int>(min.v1 - so[i].v2 * nd.v2 + so[i].v1, so[i].v2, min.v2));
                rightseg.Update(so[i].v2, new Pair<long, int>(long.MaxValue, -1));
            }
        }
        edge.Sort();
        var uf = UnionFind<int>.Make(nd.v1);
        var res = 0L;
        foreach (var e in edge)
            if (!uf.IsSame(e.v2, e.v3))
            {
                res += e.v1;
                uf.Union(e.v2, e.v3);
            }
        WriteLine(res);
    }
}

public class Input
{
    public static string read => ReadLine().Trim();
    public  static int[] ar => Array.ConvertAll(read.Split(' '), int.Parse);
    public  static int num => ToInt32(read);
    public static long[] arL => Array.ConvertAll(read.Split(' '), long.Parse);
    public  static long numL => ToInt64(read);
    public static char[][] gred(int h) 
        => Enumerable.Repeat(0, h).Select(v => read.ToCharArray()).ToArray();
    public static int[][] ar2D(int num)
        => Enumerable.Repeat(0, num).Select(_ => ar).ToArray();
    public static long[][] arL2D(int num)
        => Enumerable.Repeat(0, num).Select(_ => arL).ToArray();
    public static T getValue<T>(string g)
    {
        var t = typeof(T);
        if (t == typeof(int))
            return (T)(object)int.Parse(g);
        if (t == typeof(long))
            return (T)(object)long.Parse(g);
        if (t == typeof(string))
            return (T)(object)g;
        if (t == typeof(char))
            return (T)(object)char.Parse(g);
        if (t == typeof(double))
            return (T)(object)double.Parse(g);
        if (t == typeof(bool))
            return (T)(object)bool.Parse(g);
        return default(T);
    }
    public const long Inf = (long)1e18;
    public const double eps = 1e-6;
    public  const string alfa = "abcdefghijklmnopqrstuvwxyz";
    public  const int MOD = 1000000007;
}

public class UnionFind<T>
{
    private class Vertex
    {
        public T Key { get; set; }
        public Vertex Parent { get; set; }
        public int Rank { get; set; }
        public int Size { get; set; }
        public Vertex(T key, Vertex Parent = null, int rank = 0)
        {
            this.Key = key;
            this.Parent = Parent;
            this.Rank = rank;
        }
    }
    private readonly Dictionary<T, Vertex> dics;

    public UnionFind()
    {
        dics = new Dictionary<T, Vertex>();
    }
    
    public T Parent(T key)
        => FindSet(dics[key].Parent).Key;
    public int Size(T key)
        => FindSet(dics[key].Parent).Size;

    public bool IsSame(T key1, T key2)
    {
        if (!dics.ContainsKey(key1) || !dics.ContainsKey(key2))
            return false;
        return ReferenceEquals(FindSet(dics[key1]),FindSet(dics[key2]));
    }

    public bool MakeSet(T key)
    {
        if (dics.ContainsKey(key))
            return false;
        dics[key] = new Vertex(key);
        dics[key].Parent = dics[key];
        dics[key].Size = 1;
        return true;
    }

    public bool Union(T key1, T key2)
    {
        if (!dics.ContainsKey(key1) || !dics.ContainsKey(key2))
            return false;
        if (IsSame(key1, key2)) return false;
        Link(FindSet(dics[key1]), FindSet(dics[key2]));
        return true;
    }

    public static UnionFind<int> Make(int num, int eg = 0)
    {
        var uf = new UnionFind<int>();
        for (var i = 0; i < num; i++)
            uf.MakeSet(i);
        for (var i = 0; i < eg; i++)
        {
            var inp = Input.ar;
            inp[0]--;inp[1]--;
            uf.Union(inp[0], inp[1]);
        }
        return uf;
    }

    private void Link(Vertex vex1, Vertex vex2)
    {
        if (vex1.Rank > vex2.Rank)
        {
            vex2.Parent = vex1;
            vex1.Size += vex2.Size;
        }
        else
        {
            vex1.Parent = vex2;
            vex2.Size += vex1.Size;
            if (vex1.Rank == vex2.Rank)
                vex2.Rank++;
        }
    }

    private Vertex FindSet(Vertex vex)
    {
        if (!ReferenceEquals(vex.Parent, vex))
            vex.Parent = FindSet(vex.Parent);
        return vex.Parent;
    }
}
public class SegmentTree<T>
{
    private readonly List<T> item;
    private readonly int _num;
    private readonly Func<T, T, T> _func;
    private readonly Func<T, T, T> updateFunc;
    private readonly T _init;

    private int Parent(int index)
        => (index - 1) / 2;
    private int Left(int index)
        => 2 * index + 1;
    private int Right(int index)
        => 2 * (index + 1);

    public SegmentTree(int num, T init, Func<T, T, T> func, Func<T, T, T> updateFunc = null)
    {
        _func = func;
        _num = 1;
        _init = init;
        this.updateFunc = updateFunc ?? ((T val1, T val2) => val2);
        while (_num <= num)
            _num *= 2;
        item = new List<T>(2 * _num - 1);
        for (var i = 0; i < 2 * _num - 1; i++)
            item.Add(init);
    }
    public void Update(int index, T value)
    {
        index += _num - 1;
        item[index] = updateFunc(item[index], value);
        while (index > 0)
        {
            index = Parent(index);
            item[index] = _func(item[Left(index)], item[Right(index)]);
        }
    }
    public void Update(int left, int right, T value)
        => Update(left, right, 0, 0, _num, value);
    private void Update(int left, int right, int k, int l, int r, T value)
    {
        if (r <= left || right <= l) return;
        if (left <= l && r <= right) item[k] = updateFunc(item[k], value);
        else
        {
            Update(left, right, Left(k), l, (l + r) / 2, value);
            Update(left, right, Right(k), (l + r) / 2, r, value);
        }
    }
    public T Query(int index)
    {
        index += _num - 1;
        var value = _func(_init, item[index]);
        while (index > 0)
        {
            index = Parent(index);
            value = _func(value, item[index]);
        }
        return value;
    }
    public T Query(int left, int right)
        => Query(left, right, 0, 0, _num);
    private T Query(int left, int right, int k, int l, int r)
    {
        if (r <= left || right <= l) return _init;
        if (left <= l && r <= right) return item[k];
        else
            return _func(Query(left, right, Left(k), l, (l + r) / 2), Query(left, right, Right(k), (l + r) / 2, r));
    }
}
public class Pair<T1, T2> : IComparable<Pair<T1, T2>>
{
    public T1 v1 { get; set; }
    public T2 v2 { get; set; }
    public Pair() : this(default(T1), default(T2)) { }
    public Pair(T1 v1, T2 v2)
    { SetValue(v1, v2); }

    public int CompareTo(Pair<T1, T2> p)
    {
        var c = Comparer<T1>.Default.Compare(v1, p.v1);
        if (c == 0)
            c = Comparer<T2>.Default.Compare(v2, p.v2);
        return c;
    }
    public void SetValue(T1 v1,T2 v2) { this.v1 = v1;this.v2 = v2; }
    public static Pair<T1, T2> makePair()
    {
        var r = ReadLine().Split(' ');
        return new Pair<T1, T2>(Input.getValue<T1>(r[0]), Input.getValue<T2>(r[1]));
    }
    public override string ToString()
        => $"{v1.ToString()} {v2.ToString()}";
}

public class Pair<T1, T2, T3> : Pair<T1, T2>, IComparable<Pair<T1, T2, T3>>
{
    public T3 v3 { get; set; }
    public Pair() : base() { v3 = default(T3); }
    public Pair(T1 v1, T2 v2, T3 v3) : base()
    { SetValue(v1, v2, v3); }
    
    public int CompareTo(Pair<T1, T2, T3> p)
    {
        var c = base.CompareTo(p);
        if (c == 0)
            c = Comparer<T3>.Default.Compare(v3, p.v3);
        return c;
    }
    public void SetValue(T1 v1, T2 v2, T3 v3)
    {
        base.SetValue(v1, v2);
        this.v3 = v3;
    }
    public new static Pair<T1, T2, T3> makePair()
    {
        var r = ReadLine().Split(' ');
        return new Pair<T1, T2, T3>(Input.getValue<T1>(r[0]), Input.getValue<T2>(r[1]), Input.getValue<T3>(r[2]));
    }
    public override string ToString()
        => $"{base.ToString()} {v3.ToString()}";
}

