output_description: Print the answer as an integer.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
      A_0 A_1 A_2 \cdots A_N
attempt: N = int(input())
  A = list(map(int, input().split()))
  result = 0
  ver = []
  for n in reversed(range(0, N + 1)):
      if n == len(A) - 1:
          ver.append(A[n])
      elif A[n] == 0:
          if n**2 < ver[len(A) - n - 2]:
              ver.append(int(ver[len(A) - n - 2] / 2))
          else:
              ver.append(ver[len(A) - n - 2])
      elif A[n] != 0:
          if n**2 < ver[len(A) - n - 2]:
              ver.append(int(ver[len(A) - n - 2] / 2) + A[n])
          else:
              ver.append(ver[len(A) - n - 2] + A[n])
  
  
  print(sum(ver))
  
problem_description: Statement
  
  Given is an integer sequence of length N+1: A_0, A_1, A_2, \ldots, A_N. Is
  there a binary tree of depth N such that, for each d = 0, 1, \ldots, N, there
  are exactly A_d leaves at depth d? If such a tree exists, print the maximum
  possible number of vertices in such a tree; otherwise, print -1.
samples: [{"input": "3\n    0 1 1 2", "output": "7\n    \n\nBelow is the tree with the maximum possible number of vertices. It has seven\nvertices, so we should print 7.\n\n![0d8d99d13df036f23b0c9fcec52b842b.png](https://img.atcoder.jp/nomura2020/0d8d99d13df036f23b0c9fcec52b842b.png)\n\n* * *"}, {"input": "4\n    0 0 1 0 2", "output": "10\n    \n\n* * *"}, {"input": "2\n    0 3 1", "output": "-1\n    \n\n* * *"}, {"input": "1\n    1 1", "output": "-1\n    \n\n* * *"}, {"input": "10\n    0 0 1 1 2 3 5 8 13 21 34", "output": "264"}]