import std.stdio;
import std.string;
import std.format;
import std.conv;
import std.typecons;
import std.algorithm;
import std.functional;
import std.bigint;
import std.numeric;
import std.array;
import std.math;
import std.range;
import std.container;
import std.concurrency;
import std.traits;
import std.uni;
import core.bitop : popcnt;
alias Generator = std.concurrency.Generator;

enum long INF = long.max/3;
enum long MOD = 10L^^9+7;

void main() {
  long N, D;
  scanln(N, D);
  auto as = readln.split.to!(long[]).enumerate.array.sort!"a.value<b.value".array;
  long[] bs = new long[N];
  foreach(i, a; as) {
    bs[a.index] = i;
  }

  auto prim = Prim!long(N);

  auto seg1 = RMQ!long(N);
  foreach(ia; 0..N) {
    long i = bs[ia];
    auto a = as[i];
    {
      long v = seg1.query(0, i);
      if (v < long.max) {
        long j = seg1.queryIndex(0, i);
        prim.addEdge(i, j, v + a.index*D + a.value);
      }
    }
    {
      long v = seg1.query(i+1, N);
      if (v < long.max) {
        long j = seg1.queryIndex(i+1, N);
        prim.addEdge(i, j, v + a.index*D + a.value);
      }
    }
    seg1.update(i, a.value - a.index*D);
  }

  auto seg2 = RMQ!long(N);
  foreach_reverse(ia; 0..N) {
    long i = bs[ia];
    auto a = as[i];
    {
      long v = seg2.query(0, i);
      if (v < long.max) {
        long j = seg2.queryIndex(0, i);
        prim.addEdge(i, j, v - a.index*D + a.value);
      }
    }
    {
      long v = seg2.query(i+1, N);
      if (v < long.max) {
        long j = seg2.queryIndex(i+1, N);
        prim.addEdge(i, j, v - a.index*D + a.value);
      }
    }
    seg2.update(i, a.value + a.index*D);
  }

  prim.solve.writeln;
}

// プリム法
// O(E+VlogV)
// 無向グラフの最小全域木問題
struct Prim(T, T inf = T.max) {

private:
  Vertex[] _vertices;

public:
  this(size_t size) {
    _vertices.length = size;
    foreach(i; 0..size) {
      _vertices[i] = new Vertex(i);
    }
  }

  void addEdge(size_t start, size_t end, T weight) {
    _vertices[start].edges ~= Edge(start, end, weight);
    _vertices[end].edges   ~= Edge(end, start, weight);
  }

  T solve() {
    _vertices.front.cost = 0;
    auto tree = redBlackTree!(
      "a.cost==b.cost ? a.index<b.index : a.cost<b.cost",
      true,
      Vertex
    )(_vertices.front);
    while(!tree.empty) {
      Vertex v = tree.front;
      v.used = true;
      tree.removeFront;
      v.edges.each!((Edge e) {
        if (_vertices[e.end].used) return;
        tree.removeKey(_vertices[e.end]);
        _vertices[e.end].cost = min(_vertices[e.end].cost, e.weight);
        tree.insert(_vertices[e.end]);
      });
    }
    return _vertices.map!"a.cost".sum;
  }

private:
  class Vertex {
    size_t index;
    bool used;
    T cost = inf;
    Edge[] edges;
    this(size_t index) {
      this.index = index;
    }
    override string toString() const {return "";} // for old compilers
  }
  struct Edge {
    size_t start;
    size_t end;
    T weight;
  }
}


// RMQ (Range Minimum Query)
alias RMQ(T) = SegTree!(T, (a, b) => a<b ? a:b, T.max);

// SegTree (Segment Tree)
struct SegTree(T, alias fun, T initValue)
  if (is(typeof(fun(T.init, T.init)) : T)) {

private:
  Node[] _data;
  size_t _size;
  size_t _l, _r;

public:
  // size ... データ数
  // initValue ... 初期値(例えばRMQだとINF)
  this(size_t size) {
    init(size);
  }

  // 配列で指定
  this(T[] ary) {
    init(ary.length);
    update(ary);
  }

  // O(N)
  void init(size_t size){
    _size = 1;
    while(_size < size) {
      _size *= 2;
    }
    _data.length = _size*2-1;
    _data[] = Node(size_t.max, initValue);
    _l = 0;
    _r = size;
  }

  // i番目の要素をxに変更
  // O(logN)
  void update(size_t i, T x) {
    size_t index = i;
    i += _size-1;
    _data[i] = Node(index, x);
    while(i > 0) {
      i = (i-1)/2;
      Node nl = _data[i*2+1];
      Node nr = _data[i*2+2];
      _data[i] = select(nl, nr);
    }
  }

  // 配列で指定
  // O(N)
  void update(T[] ary) {
    foreach(i, e; ary) {
      _data[i+_size-1] = Node(i, e);
    }
    foreach(i; (_size-1).iota.retro) {
      Node nl = _data[i*2+1];
      Node nr = _data[i*2+2];
      _data[i] = select(nl, nr);
    }
  }

  // 区間[a, b)でのクエリ (値の取得)
  // O(logN)
  T query(size_t a, size_t b) {
    return queryRec(a, b, 0, 0, _size).value;
  }

  // 区間[a, b)でのクエリ (indexの取得)
  // O(logN)
  size_t queryIndex(size_t a, size_t b) out(result) {
    // fun == (a, b) => a+b のようなときはindexを聞くとassertion
    assert(result != size_t.max);
  } body {
    return queryRec(a, b, 0, 0, _size).index;
  }

  private Node queryRec(size_t a, size_t b, size_t k, size_t l, size_t r) {
    if (b<=l || r<=a) return Node(size_t.max, initValue);
    if (a<=l && r<=b) return _data[k];
    Node nl = queryRec(a, b, k*2+1, l, (l+r)/2);
    Node nr = queryRec(a, b, k*2+2, (l+r)/2, r);
    return select(nl, nr);
  }

  private Node select(Node nl, Node nr) {
    T v = fun(nl.value, nr.value);
    if (nl.value == v) {
      return nl;
    } else if (nr.value == v) {
      return nr;
    } else {
      return Node(size_t.max, v);
    }
  }

  // O(1)
  T get(size_t i) {
    return _data[_size-1 + i].value;
  }

  // O(N)
  T[] array() {
    return _data[_l+_size-1.._r+_size-1].map!"a.value".array;
  }

private:
  struct Node {
    size_t index;
    T value;
  }
}


// ----------------------------------------------


void times(alias fun)(long n) {
  // n.iota.each!(i => fun());
  foreach(i; 0..n) fun();
}
auto rep(alias fun, T = typeof(fun()))(long n) {
  // return n.iota.map!(i => fun()).array;
  T[] res = new T[n];
  foreach(ref e; res) e = fun();
  return res;
}

T ceil(T)(T x, T y) if (isIntegral!T || is(T == BigInt)) {
  // `(x+y-1)/y` will only work for positive numbers ...
  T t = x / y;
  if (t * y < x) t++;
  return t;
}

T floor(T)(T x, T y) if (isIntegral!T || is(T == BigInt)) {
  T t = x / y;
  if (t * y > x) t--;
  return t;
}

ref T ch(alias fun, T, S...)(ref T lhs, S rhs) {
  return lhs = fun(lhs, rhs);
}
unittest {
  long x = 1000;
  x.ch!min(2000);
  assert(x == 1000);
  x.ch!min(3, 2, 1);
  assert(x == 1);
  x.ch!max(100).ch!min(1000); // clamp
  assert(x == 100);
  x.ch!max(0).ch!min(10); // clamp
  assert(x == 10);
}

mixin template Constructor() {
  import std.traits : FieldNameTuple;
  this(Args...)(Args args) {
    // static foreach(i, v; args) {
    foreach(i, v; args) {
      mixin("this." ~ FieldNameTuple!(typeof(this))[i]) = v;
    }
  }
}

void scanln(Args...)(auto ref Args args) {
  import std.meta;
  template getFormat(T) {
    static if (isIntegral!T) {
      enum getFormat = "%d";
    } else static if (isFloatingPoint!T) {
      enum getFormat = "%g";
    } else static if (isSomeString!T || isSomeChar!T) {
      enum getFormat = "%s";
    } else {
      static assert(false);
    }
  }
  enum string fmt = [staticMap!(getFormat, Args)].join(" ");
  string[] inputs = readln.chomp.split;
  foreach(i, ref v; args) {
    v = inputs[i].to!(Args[i]);
  }
}

// fold was added in D 2.071.0
static if (__VERSION__ < 2071) {
  template fold(fun...) if (fun.length >= 1) {
    auto fold(R, S...)(R r, S seed) {
      static if (S.length < 2) {
        return reduce!fun(seed, r);
      } else {
        return reduce!fun(tuple(seed), r);
      }
    }
  }
}

// cumulativeFold was added in D 2.072.0
static if (__VERSION__ < 2072) {
  template cumulativeFold(fun...)
  if (fun.length >= 1)
  {
    import std.meta : staticMap;
    private alias binfuns = staticMap!(binaryFun, fun);

    auto cumulativeFold(R)(R range)
    if (isInputRange!(Unqual!R))
    {
      return cumulativeFoldImpl(range);
    }

    auto cumulativeFold(R, S)(R range, S seed)
    if (isInputRange!(Unqual!R))
    {
      static if (fun.length == 1)
        return cumulativeFoldImpl(range, seed);
      else
        return cumulativeFoldImpl(range, seed.expand);
    }

    private auto cumulativeFoldImpl(R, Args...)(R range, ref Args args)
    {
      import std.algorithm.internal : algoFormat;

      static assert(Args.length == 0 || Args.length == fun.length,
        algoFormat("Seed %s does not have the correct amount of fields (should be %s)",
          Args.stringof, fun.length));

      static if (args.length)
        alias State = staticMap!(Unqual, Args);
      else
        alias State = staticMap!(ReduceSeedType!(ElementType!R), binfuns);

      foreach (i, f; binfuns)
      {
        static assert(!__traits(compiles, f(args[i], e)) || __traits(compiles,
            { args[i] = f(args[i], e); }()),
          algoFormat("Incompatible function/seed/element: %s/%s/%s",
            fullyQualifiedName!f, Args[i].stringof, E.stringof));
      }

      static struct Result
      {
      private:
        R source;
        State state;

        this(R range, ref Args args)
        {
          source = range;
          if (source.empty)
            return;

          foreach (i, f; binfuns)
          {
            static if (args.length)
              state[i] = f(args[i], source.front);
            else
              state[i] = source.front;
          }
        }

      public:
        @property bool empty()
        {
          return source.empty;
        }

        @property auto front()
        {
          assert(!empty, "Attempting to fetch the front of an empty cumulativeFold.");
          static if (fun.length > 1)
          {
            import std.typecons : tuple;
            return tuple(state);
          }
          else
          {
            return state[0];
          }
        }

        void popFront()
        {
          assert(!empty, "Attempting to popFront an empty cumulativeFold.");
          source.popFront;

          if (source.empty)
            return;

          foreach (i, f; binfuns)
            state[i] = f(state[i], source.front);
        }

        static if (isForwardRange!R)
        {
          @property auto save()
          {
            auto result = this;
            result.source = source.save;
            return result;
          }
        }

        static if (hasLength!R)
        {
          @property size_t length()
          {
            return source.length;
          }
        }
      }

      return Result(range, args);
    }
  }
}

// minElement/maxElement was added in D 2.072.0
static if (__VERSION__ < 2072) {
  private auto extremum(alias map, alias selector = "a < b", Range)(Range r)
  if (isInputRange!Range && !isInfinite!Range &&
    is(typeof(unaryFun!map(ElementType!(Range).init))))
  in
  {
    assert(!r.empty, "r is an empty range");
  }
  body
  {
    alias Element = ElementType!Range;
    Unqual!Element seed = r.front;
    r.popFront();
    return extremum!(map, selector)(r, seed);
  }

  private auto extremum(alias map, alias selector = "a < b", Range,
              RangeElementType = ElementType!Range)
             (Range r, RangeElementType seedElement)
  if (isInputRange!Range && !isInfinite!Range &&
    !is(CommonType!(ElementType!Range, RangeElementType) == void) &&
     is(typeof(unaryFun!map(ElementType!(Range).init))))
  {
    alias mapFun = unaryFun!map;
    alias selectorFun = binaryFun!selector;

    alias Element = ElementType!Range;
    alias CommonElement = CommonType!(Element, RangeElementType);
    Unqual!CommonElement extremeElement = seedElement;

    alias MapType = Unqual!(typeof(mapFun(CommonElement.init)));
    MapType extremeElementMapped = mapFun(extremeElement);

    // direct access via a random access range is faster
    static if (isRandomAccessRange!Range)
    {
      foreach (const i; 0 .. r.length)
      {
        MapType mapElement = mapFun(r[i]);
        if (selectorFun(mapElement, extremeElementMapped))
        {
          extremeElement = r[i];
          extremeElementMapped = mapElement;
        }
      }
    }
    else
    {
      while (!r.empty)
      {
        MapType mapElement = mapFun(r.front);
        if (selectorFun(mapElement, extremeElementMapped))
        {
          extremeElement = r.front;
          extremeElementMapped = mapElement;
        }
        r.popFront();
      }
    }
    return extremeElement;
  }
  private auto extremum(alias selector = "a < b", Range)(Range r)
    if (isInputRange!Range && !isInfinite!Range &&
      !is(typeof(unaryFun!selector(ElementType!(Range).init))))
  {
    alias Element = ElementType!Range;
    Unqual!Element seed = r.front;
    r.popFront();
    return extremum!selector(r, seed);
  }
  private auto extremum(alias selector = "a < b", Range,
              RangeElementType = ElementType!Range)
             (Range r, RangeElementType seedElement)
    if (isInputRange!Range && !isInfinite!Range &&
      !is(CommonType!(ElementType!Range, RangeElementType) == void) &&
      !is(typeof(unaryFun!selector(ElementType!(Range).init))))
  {
    alias Element = ElementType!Range;
    alias CommonElement = CommonType!(Element, RangeElementType);
    Unqual!CommonElement extremeElement = seedElement;
    alias selectorFun = binaryFun!selector;

    // direct access via a random access range is faster
    static if (isRandomAccessRange!Range)
    {
      foreach (const i; 0 .. r.length)
      {
        if (selectorFun(r[i], extremeElement))
        {
          extremeElement = r[i];
        }
      }
    }
    else
    {
      while (!r.empty)
      {
        if (selectorFun(r.front, extremeElement))
        {
          extremeElement = r.front;
        }
        r.popFront();
      }
    }
    return extremeElement;
  }
  auto minElement(Range)(Range r)
    if (isInputRange!Range && !isInfinite!Range)
  {
    return extremum(r);
  }
  auto minElement(alias map, Range, RangeElementType = ElementType!Range)
           (Range r, RangeElementType seed)
  if (isInputRange!Range && !isInfinite!Range &&
    !is(CommonType!(ElementType!Range, RangeElementType) == void))
  {
    return extremum!map(r, seed);
  }
  auto minElement(Range, RangeElementType = ElementType!Range)
           (Range r, RangeElementType seed)
    if (isInputRange!Range && !isInfinite!Range &&
      !is(CommonType!(ElementType!Range, RangeElementType) == void))
  {
    return extremum(r, seed);
  }
  auto maxElement(alias map, Range)(Range r)
  if (isInputRange!Range && !isInfinite!Range)
  {
    return extremum!(map, "a > b")(r);
  }
  auto maxElement(Range)(Range r)
  if (isInputRange!Range && !isInfinite!Range)
  {
    return extremum!`a > b`(r);
  }
  auto maxElement(alias map, Range, RangeElementType = ElementType!Range)
           (Range r, RangeElementType seed)
  if (isInputRange!Range && !isInfinite!Range &&
    !is(CommonType!(ElementType!Range, RangeElementType) == void))
  {
    return extremum!(map, "a > b")(r, seed);
  }
  auto maxElement(Range, RangeElementType = ElementType!Range)
           (Range r, RangeElementType seed)
  if (isInputRange!Range && !isInfinite!Range &&
    !is(CommonType!(ElementType!Range, RangeElementType) == void))
  {
    return extremum!`a > b`(r, seed);
  }
}

// popcnt with ulongs was added in D 2.071.0
static if (__VERSION__ < 2071) {
  ulong popcnt(ulong x) {
    x = (x & 0x5555555555555555L) + (x>> 1 & 0x5555555555555555L);
    x = (x & 0x3333333333333333L) + (x>> 2 & 0x3333333333333333L);
    x = (x & 0x0f0f0f0f0f0f0f0fL) + (x>> 4 & 0x0f0f0f0f0f0f0f0fL);
    x = (x & 0x00ff00ff00ff00ffL) + (x>> 8 & 0x00ff00ff00ff00ffL);
    x = (x & 0x0000ffff0000ffffL) + (x>>16 & 0x0000ffff0000ffffL);
    x = (x & 0x00000000ffffffffL) + (x>>32 & 0x00000000ffffffffL);
    return x;
  }
}


Measured memory_bytes: 179496