Problem:
Score : 600 points

Problem 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.

Notes

A binary tree is a rooted tree such that each vertex has at most two direct children.

A leaf in a binary tree is a vertex with zero children.

The depth of a vertex v in a binary tree is the distance from the tree's root to v. (The root has the depth of 0.)

The depth of a binary tree is the maximum depth of a vertex in the tree.

Constraints

0 \leq N \leq 10^5

0 \leq A_i \leq 10^{8} (0 \leq i \leq N)

A_N \geq 1

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
A_0 A_1 A_2 \cdots A_N

Output

Print the answer as an integer.

Sample Input 1

3
0 1 1 2

Sample Output 1

7

Below is the tree with the maximum possible number of vertices. It has seven vertices, so we should print 7.

Sample Input 2

4
0 0 1 0 2

Sample Output 2

10

Sample Input 3

2
0 3 1

Sample Output 3

-1

Sample Input 4

1
1 1

Sample Output 4

-1

Sample Input 5

10
0 0 1 1 2 3 5 8 13 21 34

Sample Output 5

264

Solution in Ruby (2.7.1) (judge verdict: Wrong Answer)

N = gets.to_i
A = gets.split.map(&:to_i)

unless A[0] == 0
  puts -1
  exit
end

sum_a = Array.new(N+1, 0)
sum_a[-1] = A[-1]
(N-1).downto(0) do |i|
  sum_a[i] = sum_a[i+1] + A[i]
end

b = Array.new(N+1, 0)
b[0] = 1

ans = 1

1.upto(N) do |i|
  if i == N
    ans += A[N]
    next
  end
  b_v = [sum_a[i + 1], 2 * b[i-1] - A[i]].min
  b[i] = b_v

  unless b[i-1] <= A[i] + b[i] && A[i] + b[i] <= 2 * b[i]
    puts -1
    exit
  end
  ans += A[i] + b[i]
end

puts ans