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: Wrong Answer)

#include<iostream>
#include<string>
using namespace std;
#define ll long long
#define INF 200000000
ll n,a[100050],min1[100050],min2[100050];
signed main(){
	cin>>n>>a[0];
	if(a[0]!=0){cout<<-1<<endl;return 0;
	}
	for(ll i=1;i<=n;i++)cin>>a[i];
	min1[0]=1;
	min2[n]=a[n];
	for(ll i=1;i<=n;i++){
		min1[i]=min1[i-1]*2-2*a[i-1];
	}
	if(min1[n]<a[n]){cout<<-1<<endl;return 0;
	}
	for(ll i=n-1;i>=0;i--){
		min2[i]=min2[i+1]+a[i];
	}
	if(min2[0]<1){cout<<-1<<endl;return 0;
	}
	for(int i=0;i<=n;i++){
		if(min1[i]<a[i]&&min2[i]<a[i]){
			cout<<-1<<endl;return 0;
		}
		if(min1[i]<a[i])min1[i]=INF;
		if(min2[i]<a[i])min2[i]=INF;
	}
	ll cnt=0;
	for(ll i=0;i<=n;i++){
		cnt+=min(min1[i],min2[i]);
	}cout<<cnt<<endl;
}