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())
A=list(map(int, input().split()))

ans=0
bef=0

tmp=[]

for i in range(N+1):
    if i==0:
        if A[0]==1:
            bef=0
        elif A[0]>1:
            print("-1")
            exit()
        elif N==0 and A[0]==0:
            print("-1")
            exit()
        else:
            bef=1
        tmp.append(1)
        continue
    elif (bef*2-A[i])>=0:
        bef=bef*2-A[i]
        tmp.append(bef)
    else:
        print("-1")
        exit()

for i in range(N+1):
    current=A[-(i+1)]
    if i==0:
        bef=current
        ans+=current
        continue
    else:
        tmpp = tmp[-(i+1)]
        if current+bef > tmpp:
            ans+=tmpp+current
            bef=tmpp+current
        else:
            ans+=current+bef
            bef=current+bef

print(ans)