import sys
from collections import defaultdict as dd
input = sys.stdin.readline
N, D = map(int, input().split())
a = list(map(int, input().split()))
dl = [0] * N
dr = [0] * N
base = 10 ** 6
for i in range(N):
  dl[i] = ((N - i) * D + a[i]) * base + i
  dr[i] = (i * D + a[i]) * base + i
e = dd(list)
class SegTree:
  def segfunc(self, x, y):
    return min(x, y)
  def __init__(self, n, ide_ele, init_val):
    #####単位元######
    self.ide_ele = ide_ele
    #num:n以上の最小の2のべき乗
    self.num = 2 ** (n - 1).bit_length()
    self.seg = [self.ide_ele] * 2 * self.num
    #set_val
    for i in range(n):
      self.seg[i + self.num - 1] = init_val[i]    
    #built
    for i in range(self.num - 2, -1, -1) :
      self.seg[i] = self.segfunc(self.seg[2 * i + 1], self.seg[2 * i + 2]) 
  def update(self, k, x):
    k += self.num - 1
    self.seg[k] = x
    while k + 1:
      k = (k - 1) // 2
      self.seg[k] = self.segfunc(self.seg[k * 2 + 1], self.seg[k * 2 + 2]) 
  def query(self, p, q):
    if q <= p:
      return self.ide_ele
    p += self.num - 1
    q += self.num - 2
    res = self.ide_ele
    while q - p > 1:
      if p & 1 == 0:
        res = self.segfunc(res, self.seg[p])
      if q & 1 == 1:
        res = self.segfunc(res, self.seg[q])
        q -= 1
      p = p // 2
      q = (q - 1) // 2
    if p == q:
      res = self.segfunc(res, self.seg[p])
    else:
      res = self.segfunc(self.segfunc(res, self.seg[p]), self.seg[q])
    return res
lseg = SegTree(N, pow(10, 20), dl)
rseg = SegTree(N, pow(10, 20), dr)
for i in range(N):
  l = lseg.query(0, i)
  r = rseg.query(i + 1, N)
  e[i].append((l % base, a[i] + l // base - D * (N - i)))
  e[l % base].append((i, a[i] + l // base - D * (N - i)))
  e[i].append((r % base, a[i] + r // base - D * i))
  e[r % base].append((i, a[i] + r // base - D * i))
import heapq

class prim:
  def __init__(self, n, e):
    self.e = e
    self.n = n
  def MSTcost(self):
    h = []
    visited = [0] * (self.n + 1)
    ks = list(self.e.keys())
    b = pow(10, 16)
    for edge in self.e[ks[0]]:
      heapq.heappush(h, edge[1] * b + edge[0])
    res = 0
    visited[ks[0]] = 1
    while len(h):
      p = heapq.heappop(h)
      p0 = p // b
      p1 = p % b
      if visited[p1]: continue
      visited[p1] = 1
      for q in self.e[p1]:
        if visited[q[0]]:
          continue
        heapq.heappush(h, q[1] * b + q[0])
      res += p0
    return res
#print(e)
pri = prim(N, e)
print(pri.MSTcost())