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 Python (3.8.2) (judge verdict: Wrong Answer)

n = int( input() )
a = list( map( int, input().split() ) )

sum_a = [ sum( a ) ]
for d in range( 1, n + 1 ):
    sum_a_next = sum_a[ -1 ] - a[ d - 1 ]
    sum_a.append( sum_a_next )
d_vertex = [ 0 for d in range( n + 1 ) ]

d_vertex[ 0 ] = 1
num_of_v = d_vertex[ 0 ]
for d in range( 1, n + 1 ):
    d_vertex[ d ] = min( sum_a[d], ( d_vertex[ d - 1 ] - a[ d - 1 ] ) * 2 )
    if d_vertex[ d ] <= 0:
        print( -1 )
        exit()
    num_of_v += d_vertex[ d ]
    # print( d, d_vertex )

print( num_of_v )