#include <bits/stdc++.h>

#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/detail/standard_policies.hpp>
using namespace __gnu_pbds;

#if !ONLINE_JUDGE
#define debug
#endif

using namespace std;
 
/*******  All Required define Pre-Processors and typedef Constants *******/
#define mem(a, b) memset(a, (b), sizeof(a))
#define repd(i,k) for(int i=k;i>=0;i--)
#define rep(i,k) for(int i=0;i<k;i++)
#define repn(i,k1,k2) for(ll i=k1;i<k2;i++)
#define sz(x) (ll)(x).size()
#define ff first
#define ss second

#define all(cont) cont.begin(), cont.end()
#define rall(cont) cont.end(), cont.begin()
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define INF (int)1e9
#define EPS 1e-9
#define PI 3.1415926535897932384626433832795
#define MOD 1000000007
#define ee6 (ll)1000001
#define ee5 (ll)100001

#define trav(a, v) for(auto& a : v)

#define tt ll t;cin>>t; while(t--)
typedef long long int ll;
 
typedef pair<ll, ll> pr;
typedef vector<ll> vi;
typedef vector<string> vs;
typedef vector<pr> vpr;
typedef vector<vpr>vvpr;
typedef vector<vi> vvi;

//*X.find_by_order(2) element at index=2
//X.order_of_key(1) how many elements strictly less than 1

template <typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag,
    tree_order_statistics_node_update>;

#ifdef debug
#define dbg(...) { cerr<<"[ "; dump(#__VA_ARGS__, __VA_ARGS__);}
#undef endl
template <typename Arg1,typename Arg2>
ostream& operator << (ostream& out, const pair<Arg1,Arg2> &x) {
    return out<<"("<<x.ff<<","<<x.ss<<")";
}
 
template <typename Arg1>
ostream& operator << (ostream& out, const vector<Arg1> &a) {
    out<<"[";for(const auto &x:a)out<<x<<",";return out<<"]";
}
 
template <typename Arg1>
ostream& operator << (ostream& out, const set<Arg1> &a) {
    out<<"[";for(const auto &x:a)out<<x<<",";return out<<"]";
}
 
template <typename Arg1,typename Arg2>
ostream& operator << (ostream& out, const map<Arg1,Arg2> &a) {
    out<<"[";for(const auto &x:a)out<<x<<",";return out<<"]";
}
 
template <typename Arg1,typename Arg2>
ostream& operator << (ostream& out, const unordered_map<Arg1,Arg2> &a) {
    out<<"[";for(const auto &x:a)out<<x<<",";return out<<"]";
} 
 
template <typename Arg1>
void dump(const string name, Arg1&& arg1){
    cerr << name << " : " << arg1 << " ] " << endl;
}
 
template <typename Arg1, typename... Args>
void dump(const string names, Arg1&& arg1, Args&&... args){
    const string name = names.substr(0,names.find(','));
    cerr<<name<<" : "<<arg1<<" | ";
    dump(names.substr(1+(int)name.size()), args...);
}
#else
    #define dbg(args...)
#endif

void compress(vi &temp){
	int n=temp.size();vi v=temp;sort(all(v));v.erase(unique(all(v)),v.end());map<ll,ll>mt;
	for(int j=0;j<v.size();j++)mt[v[j]]=j;
	for(auto &e:temp)e=mt[e];
}
ll powmod(ll x, ll y) 
{ 
    ll res = 1;  
    x = x % MOD;
    while (y > 0) 
    { 
        if (y & 1) 
  	      res = (res*x) % MOD; 
        y = y>>1; // y = y/2 
        x = (x*x) % MOD;   
    } 
    return res; 
} 

ll a[ee5+5];
pr allow[ee5+5];
pr allow2[ee5+5];
int main()
{
	#if !ONLINE_JUDGE
	//freopen("in.txt","r",stdin);
	#endif
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
 	
 	ll n;cin>>n;
 	for(ll i=0;i<=n;i++)cin>>a[i]; 	

 	
 	
 	ll l=1,r=1;
 	
 	for(ll i=0;i<=n;i++){ 		 		
 		if(a[i]>r){
 			cout<<"-1";exit(0);
 		}
 		else if(a[i]<l){
 			allow[i]=mp(l,r);
 		}
 		else{
 			allow[i]=mp(a[i],r);
 		}
 		l-=a[i],r-=a[i];
 		r=r*2;
 		r=min(r,(ll)1e17);
 		l=max(0ll,l);
 	}
 	
 	l=0,r=0;
 	for(ll i=n;i>=0;i--){
 		l+=a[i],r+=a[i];
 		allow2[i]={l,r};
 		l=(l+1)/2;
 	}

 	ll ans=0;
 	for(ll i=0;i<=n;i++){
 		if(allow[i].ss<allow2[i].ff or allow[i].ff>allow2[i].ss){
 			cout<<"-1";exit(0);
 		}
 		ans+=min(allow[i].ss,allow2[i].ss);
 	}
 	cout<<ans;
}

Measured memory_bytes: 7564