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: Accepted)

N = gets.to_i
sum = 0
leaf = gets.split.map(&:to_i)
leaf.map{|n| sum += n}
done = false
count = 0
nodes = []
answer = -1

if N == 0 
    if leaf.first == 0
        puts 0
        return
    end
    if leaf.first == 1
        puts 1
        return
    end
    puts answer
    return
end    

leaf.each_with_index do | n , i |
    if i == 0
        nodes << 1
        next
    end

    max_next_nodes = ( nodes[ i - 1 ] - leaf[ i - 1 ] ) * 2
    if  max_next_nodes  < leaf [i]
        break
    end

    sum = sum - leaf [ i-1 ]
    
    
    if sum <= max_next_nodes
        nodes << sum
        next
    end

    nodes << max_next_nodes

end

if nodes.length == leaf.length
    done = true 
end

if ! done
    puts answer
else
    nodes.map{|n| count += n}
    puts count
end