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 C++ (GCC 9.2.1) (judge verdict: Runtime Error)

#include<bits/stdc++.h>
using namespace std;

int N;
long long int A[100010];
long long int SVertex[100010];
long long int ans = -1;

long long int My_Function(long long int Vertex, long long int depth){

    SVertex[depth] = Vertex;

    if(depth == N){
        if(Vertex == A[N]){
            for(int i=0; i<N ; i++){
                ans += SVertex[i];
            }
        }
    }else{

        if(Vertex <= A[depth]){

        }else{
            for(int i = 0; i <= Vertex - A[depth] ; i++){
                My_Function(Vertex - A[depth] + i,depth + 1);
            }
        }
    }
}

int main(){
    cin >> N;
    for (int i = 0; i <= N ; i++){
        cin >> A[i];
    }
    My_Function(1,0);
    cout << ans << endl;
}