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 PyPy3 (7.3.0) (judge verdict: Wrong Answer)

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


ans = 0
nodes_min = [0] * (n + 1)
nodes_max = [0] * (n + 1)
nodes_min[n] = leaves[n]
nodes_max[n] = leaves[n]

for depth in range(n, 0, -1):
    root_min = nodes_min[depth] // 2 + nodes_min[depth] % 2
    nodes_min[depth - 1] = leaves[depth - 1] + root_min
    root_max = nodes_max[depth]
    nodes_max[depth - 1] = leaves[depth - 1] + root_max
nodes = [0] * (n + 1)
nodes[0] = 1
for depth in range(n):
    roots = nodes[depth]-leaves[depth]
    if roots <= 0:
        print(-1)
        break
    nodes[depth + 1] = min(roots * 2, nodes_max[depth + 1])
else:
    print(sum(nodes))