#include<algorithm>//sort,二分探索,など
#include<bitset>//固定長bit集合
#include<cmath>//pow,logなど
#include<complex>//複素数
#include<deque>//両端アクセスのキュー
#include<functional>//sortのgreater
#include<iomanip>//setprecision(浮動小数点の出力の誤差)
#include<iostream>//入出力
#include<iterator>//集合演算(積集合,和集合,差集合など)
#include<map>//map(辞書)
#include<numeric>//iota(整数列の生成),gcdとlcm(c++17)
#include<queue>//キュー
#include<set>//集合
#include<stack>//スタック
#include<string>//文字列
#include<unordered_map>//イテレータあるけど順序保持しないmap
#include<unordered_set>//イテレータあるけど順序保持しないset
#include<utility>//pair
#include<vector>//可変長配列

#define rep(i,n) for (int i = 0; i < (n); ++i)
#define erep(i,n) for (int i = 1; i <= (n); ++i)
#define brep(i,n) for (int i = n; i >= 0; i--)
#define pb push_back
using namespace std;
using P = pair<int,int>;
using ll = long long;
using Graph = vector<vector<int> > ;

const double PI=3.14159265358979323846;
const int INF = 100005;
const int MAX_K = 55;
const int MAX_W = 200005; 
const int MAX = 510000;
const int MOD = 1000000007;
long long fac[MAX], finv[MAX], inv[MAX];
ll dp[100005];


// ユークリッド互除法
unsigned gcd(unsigned a, unsigned b) {
  while(1) {
    if(a < b) swap(a, b);
    if(!b) break;
    a %= b;
  }
  return a;
}

// テーブルを作る前処理
void COMinit() {
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (int i = 2; i < MAX; i++){
        fac[i] = fac[i - 1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD / i) % MOD;
        finv[i] = finv[i - 1] * inv[i] % MOD;
    }
}

// 二項係数計算
long long COM(int n, int k){
    if (n < k) return 0;
    if (n < 0 || k < 0) return 0;
    return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}

/*
int main() {
    // 前処理
    COMinit();

    // 計算例
    cout << COM(100000, 50000) << endl;
}
*/

struct mint {
  ll x; // typedef long long ll;
  mint(ll x=0):x((x%MOD+MOD)%MOD){}
  mint operator-() const { return mint(-x);}
  mint& operator+=(const mint a) {
    if ((x += a.x) >= MOD) x -= MOD;
    return *this;
  }
  mint& operator-=(const mint a) {
    if ((x += MOD-a.x) >= MOD) x -= MOD;
    return *this;
  }
  mint& operator*=(const mint a) { (x *= a.x) %= MOD; return *this;}
  mint operator+(const mint a) const { return mint(*this) += a;}
  mint operator-(const mint a) const { return mint(*this) -= a;}
  mint operator*(const mint a) const { return mint(*this) *= a;}
  mint pow(ll t) const {
    if (!t) return 1;
    mint a = pow(t>>1);
    a *= a;
    if (t&1) a *= *this;
    return a;
  }

  // for prime MOD
  mint inv() const { return pow(MOD-2);}
  mint& operator/=(const mint a) { return *this *= a.inv();}
  mint operator/(const mint a) const { return mint(*this) /= a;}
};
istream& operator>>(istream& is, const mint& a) { return is >> a.x;}
ostream& operator<<(ostream& os, const mint& a) { return os << a.x;}

struct UnionFind {
    vector<int> par;
    vector<int> rank;
    vector<ll> Size;
    UnionFind(int n = 1) {
        init(n);
    }
 
    void init(int n = 1) {
        par.resize(n + 1); rank.resize(n + 1); Size.resize(n + 1);
        for (int i = 0; i <= n; ++i) par[i] = i, rank[i] = 0, Size[i] = 1;
    }
 
    int root(int x) {
        if (par[x] == x) {
            return x;
        }
        else {
            int r = root(par[x]);
            return par[x] = r;
        }
    }
 
    bool issame(int x, int y) {
        return root(x) == root(y);
    }
 
    bool merge(int x, int y) {
        x = root(x); y = root(y);
        if (x == y) return false;
        if (rank[x] < rank[y]) swap(x, y);
        if (rank[x] == rank[y]) ++rank[x];
        par[y] = x;
        Size[x] += Size[y];
        return true;
    }
 
    ll size(int x){
        return Size[root(x)];
    }
};

int main(){
  int n;
  cin >> n;
  ll leave[n+1];
  ll all = 0;
  rep(i,n+1){
    ll a;
    cin >> a;
    all += a;
    leave[i] = a;
  }

  if(n == 0){
    if(leave[0] == 1){
      cout << 1 << endl;
    }else{
      cout << -1 << endl;
    }
    return 0;
  }
  if(leave[0] != 0){
    cout << -1 << endl;
    return 0;
  }

  ll root[n+1];
  ll limit[n+1];
  root[0] = 1;
  limit[0] = all;
  for(int i =1; i<n+1; i++){
    limit[i] = limit[i-1] - leave[i];
  }

  for(int i = 1; i < n+1; i++){
    
    if(root[i-1]*2 < leave[i]){
      cout << -1 << endl;
      return 0;
    }
    
    root[i] = min(root[i-1]*2 - leave[i],limit[i]);
  }

  if(root[n] != 0){
    cout << -1 << endl;
    return 0;
  }

  ll ans = 0;
  rep(i,n+1){
    ans += root[i];
    ans += leave[i];
  }

  cout << ans << endl;

}

Measured memory_bytes: 5944