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 = [int(a) for a in input().split()]

ans = 0
prev = 1
L = [0]*(N+1)
L[0] = 1
for i in range(1, N+1):
    if prev*2 > A[i]:
        prev = prev*2-A[i]
    elif prev*2 == A[i] and i == N:
        continue
    else:
        ans = -1
        break
    L[i] = prev
    if prev > 10**10:
        for j in range(i+1, N+1):
            L[j] = "inf"
        break

if A[0] > 0:
    ans = -1

if ans == 0:
    L = [0]*(N+2)
    for i in range(N+1):
        L[i+1] = L[i]+A[i]
    prev = 1
    ans = 1
    for i in range(1, N+1):
        d = min(2*prev, L[-1]-L[i])
        ans += d
        prev = d-A[i]
        
print(ans)