output_description: Print the answer.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N X
      x_1 x_2 ... x_{N}
attempt: n, m = map(int, input().split())
  x = list(map(int, input().split()))
  x.reverse()
  cum = [0] * (n + 1)
  for i in range(n):
      cum[i + 1] = cum[i] + x[i]
  mincost = 2 * n * m + 5 * cum[n]
  for k in range(1, n):
      cost = m * (n + k)
      for i in range(n // k):
          cost += (cum[(i + 1) * k] - cum[i * k]) * max(5, 3 + i * 2)
      cost += (cum[n] - cum[n // k * k]) * max(5, 3 + n // k * 2)
      mincost = min(mincost, cost)
  print(mincost)
  
problem_description: Statement
  
  Snuke has decided to use a robot to clean his room.
  
  There are N pieces of trash on a number line. The i-th piece from the left is
  at position x_i. We would like to put all of them in a trash bin at position
  0.
  
  For the positions of the pieces of trash, 0 < x_1 < x_2 < ... < x_{N} \leq
  10^{9} holds.
  
  The robot is initially at position 0. It can freely move left and right along
  the number line, pick up a piece of trash when it comes to the position of
  that piece, carry any number of pieces of trash and put them in the trash bin
  when it comes to position 0. It is not allowed to put pieces of trash anywhere
  except in the trash bin.
  
  The robot consumes X points of energy when the robot picks up a piece of
  trash, or put pieces of trash in the trash bin. (Putting any number of pieces
  of trash in the trash bin consumes X points of energy.) Also, the robot
  consumes (k+1)^{2} points of energy to travel by a distance of 1 when the
  robot is carrying k pieces of trash.
  
  Find the minimum amount of energy required to put all the N pieces of trash in
  the trash bin.
samples: [{"input": "2 100\n    1 10", "output": "355\n    \n\n  * Travel to position 10 by consuming 10 points of energy.\n  * Pick up the piece of trash by consuming 100 points of energy.\n  * Travel to position 1 by consuming 36 points of energy.\n  * Pick up the piece of trash by consuming 100 points of energy.\n  * Travel to position 0 by consuming 9 points of energy.\n  * Put the two pieces of trash in the trash bin by consuming 100 points of energy.\n\nThis strategy consumes a total of 10+100+36+100+9+100=355 points of energy.\n\n* * *"}, {"input": "5 1\n    1 999999997 999999998 999999999 1000000000", "output": "19999999983\n    \n\n* * *"}, {"input": "10 8851025\n    38 87 668 3175 22601 65499 90236 790604 4290609 4894746", "output": "150710136\n    \n\n* * *"}, {"input": "16 10\n    1 7 12 27 52 75 731 13856 395504 534840 1276551 2356789 9384806 19108104 82684732 535447408", "output": "3256017715"}]