#include <bits/stdc++.h>
#include <unistd.h>
#include <sys/time.h>
#include <stdlib.h>
 
using namespace std;
 
typedef long long ll;
typedef pair<ll,ll> P;
typedef pair<P, ll> T;
typedef pair<long double , ll> Ps;
 
long long int INF = 2e18;
const ll fact_table = 3200008;
double Pi = 3.1415926535897932384626;

priority_queue <ll> pql;
priority_queue <P> pqp;
priority_queue <P> bag;
//big priority queue
priority_queue <ll,vector<ll>,greater<ll> > pqls;
priority_queue <P,vector<P>,greater<P> > pqps;
//small priority queue
//top pop
 
ll dx[8]={1,0,-1,0,1,1,-1,-1};
ll dy[8]={0,1,0,-1,1,-1,-1,1};
char dir[] = "DRUL";
//↓,→,↑,←

#define endl "\n"
#ifdef ENJAPMA
    #undef endl
#endif
#define p(x) cout<<x<<endl;
#define el cout<<endl;
#define pe(x) cout<<x<<" ";
#define ps(x) cout<<fixed<<setprecision(25)<<x<<endl;
#define pu(x) cout<<(x);
#define pb push_back
#define lb lower_bound
#define ub upper_bound
#define CLEAR(a) a = decltype(a)(); 
#define pc(x) cout << x << ",";
#define rep(i, n) for (ll i = 0; i < (n); i ++)

const ll mod = 998244353ll;
// const ll mod = 1000000007ll;

ll mypow(ll a, ll b, ll mod){ll x=1;while(b){while(!(b&1)){(a*=a)%=mod;b>>=1;}(x*=a)%=mod;b--;}return x;}
void YES(bool cond){ if(cond){ p("YES");}else{ p("NO");} return;}
void Yes(bool cond){ if(cond){ p("Yes");}else{ p("No");} return;}

/*
ll fact[fact_table + 5],rfact[fact_table + 5]; 
 
void c3_init(){
    fact[0] = rfact[0] = 1;
    for(ll i=1; i<=fact_table; i++){
        fact[i] = (fact[i-1]*i) % mod;
    }
    rfact[fact_table] = mypow(fact[fact_table],mod - 2, mod);
    for(ll i=fact_table; i>=1; i--){
       rfact[i-1] = rfact[i] * i;
       rfact[i-1] %= mod;
    }
    return;}
ll c3(ll n,ll r){
    return (((fact[n] * rfact[r]) % mod ) * rfact[n-r]) % mod;}
*/

bool multicase = false;

ll n,m,num,a,b,c,d,e,h,q;
ll w, k, ans;

ll x[500005];
ll dp[500005];
P table[500005];
string s;

void solve(){
    cin >> n;
    for(ll i=0;i<=n;i++){
        cin >> x[i];
    }
    if(n == 0){
        if(x[0] != 1){
            p(-1);
            return;
        }else{
            p(1);
            return;
        }
    }
    bool dame = false;
    ll v = 1;
    ll mini = 1, maxi = 1;
    table[0].first = 1, table[0].second = 1;
    for(ll i=0;i<=n;i++){
        mini -= x[i], maxi -= x[i];
        mini = mini;
        if(maxi > 0 && 2 > INF / maxi){
            maxi = INF;
        }else{
            maxi = 2 * maxi;
        }
        if(i != n)table[i+1].first = mini, table[i+1].second = maxi;
        if(maxi < 0)dame = true;
    }
    v = 0;
    for(ll i=n;i>=0;i--){
        ll mini = table[i].first, maxi = table[i].second;
        mini -= x[i], maxi -= x[i];
        if(i != n){
            if(mini <= v && v <= maxi * 2){
                // ok
                v = min(v, maxi);
            }else{
                dame = true;
            }
        }
        v += x[i];
        ans += v;
    }
    if(dame){
        p(-1);
        return;
    }
    p(ans);

    return;
}


int main(){
    // init();
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    ll q, testcase = 1;
    if(multicase){
        cin >> q;
    }else{
        q = 1; 
    }
    while(q--){
        // pu("Case ");pu("#");pu(testcase);pu(": ");
        solve();
        testcase++;
    }
    // solve();
    return 0;
}
















Measured memory_bytes: 5944