#include <bits/stdc++.h>
#include <omp.h>

using namespace std;

typedef unsigned long long ull;
typedef long long ll;
typedef double ld;


#define int ll
#define rand shittttty_shit
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
mt19937_64 rng_64(chrono::steady_clock::now().time_since_epoch().count());


typedef pair<int, int> pii;
typedef pair<string, string> pst;
typedef pair<pii, pii> piii;
typedef vector<piii> vpii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector< vi > vvi;
typedef vector< vvi > vvvi;
typedef vector<pii> vpi;
typedef vector<short> vs;
typedef vector<vs> vvs;
typedef vector<vvs> vvvs;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<vvl> vvvl;
typedef vector<ld> vld;
typedef vector<vld> vvld;
typedef vector<vvld> vvvld;
typedef vector<string> vst;
typedef vector<vst> vvst;
typedef pair<ld, ld> pld;
typedef pair<pld, pld> pldd;
typedef vector<pld> vpd;
typedef complex<double> base;


#define inmin(a, b) a = min(a, (b))
#define inmax(a, b) a = max(a, (b))
#define my_abs(a) (((a) >= 0) ? (a) : -(a))
#define mp(a, b) make_pair(a, (b))
#define ALL(a) a.begin(),a.end()
#define RALL(a) a.rbegin(),a.rend()
#define sqr(x) ((x) * (x))
#define fori(i, n) for(int i = 0; i < int(n); ++i)
#define SZ(a) ((int)((a).size()))
#define MODIK(a) (a >= M ? a - M : a)
#define triple(T) tuple<T, T, T>
#define quad(T) tuple<T, T, T, T>
#define watch(x) cout << (#x) << " = " << x << endl;
#ifdef ART_HOME
#define cerr cout
#else
#define cerr if (false) cerr
#endif


const double PI = 2 * acos(0.0);

const string DIGITS = "0123456789";
const string ALPH = "abcdefghijklmnopqrstuvwxyz";

istream &operator >> (istream &in, pii &a)
{
    in >> a.first >> a.second;
    return in;
}


ostream &operator << (ostream &out, pii &a)
{
    out << a.first << ' ' << a.second;
    return out;
}


istream &operator >> (istream &in, pld &a)
{
    in >> a.first >> a.second;
    return in;
}


ostream &operator << (ostream &out, pld &a)
{
    out << a.first << ' ' << a.second;
    return out;
}


template <class T0, class T1>
inline ostream & operator << (ostream &out, pair<T0, T1> &a) {
    return out << "{" << a.first << ", " << a.second << "}";
}

template <class T0, class T1, class T2>
inline ostream & operator << (ostream &out, tuple<T0, T1, T2> &a) {
    return out << "{" << get<0>(a) << ", " << get<1>(a) << ", " << get<2>(a) << "}";
}

template <class T0, class T1, class T2, class T3>
inline ostream & operator << (ostream &out, tuple<T0, T1, T2, T3> &a) {
    return out << "{" << get<0>(a) << ", " << get<1>(a) <<
               ", " << get<2>(a) << ", " <<  get<3>(a) << "}";
}

template<class T>
inline ostream & operator << (ostream &out, vector<T> &a) {
    out << "[";
    fori (i, a.size())
        out << a[i] << vector<string>{", ", "]  "}[i + 1 == a.size()];
    return out;
}


void print(int a, int b, int n, vi h)
{
    ofstream cout("output.txt");
    cout << SZ(h) << ' ' << a << ' ' << b << '\n';
    for (int i = 0; i < SZ(h); ++i) {
        cout << h[i]  << ' ';
    }
    cout.close();
    exit(0);
}


inline bool break_time(ld time)
{
    return clock() > CLOCKS_PER_SEC * time;
}


ld get_rand_ld(ld l, ld r)
{
    uniform_real_distribution<double> gen(l, r);
    return gen(rng);
}


bool may(int E, ld T)
{
    if (E < 0)
        return 1;

    double eps = get_rand_ld(0, 1);
    return eps < exp(-E / T);
}


void smain();

signed main() {
    ios::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);

#ifdef ART_HOME
    freopen("input.txt", "r", stdin);
    clock_t start = clock();
#endif
    cout << setprecision(12) << fixed;
    smain();
#ifdef ART_HOME
    cout << "\nTOTAL EXECUTIOn TIME: " << float( clock () - start ) /  CLOCKS_PER_SEC << endl;
#endif
}


const int N = 500 + 10, K = 1e2 + 10, B = 1000, oo = 1e18 + 2e17, M = 1e9 + 7, LOG = 20;
const int M1 = 1000000093, x1 = 27162;
const int M2 = 1000000087, x2 = 241;
const ld pi = atan2(1, 0) * 2;


int check(int lay, const vi &kek, int label = 0, int add = 0)
{
    int n = SZ(kek) - 1;
    int cur = 0;
    int ans = 0;
    int lb = 1;

    for (int i = n; i >= 0; --i)
    {
        if (i >= lay) {
            cur += kek[i];
        }
        else if (label && i == lay - 1)
        {
            if (add < (cur + 1) / 2)
                return 1;
            else if (add > cur)
                return 0;

            cur = add;
            cur += kek[i];
        }
        else {
            cur++;
            cur >>= 1;
            cur += kek[i];
        }

        ans += cur;
        if (i <= 50 && cur > (1LL << i))
        {
            lb = 0;
            break;
        }
    }

    if (!label)
        return lb;
    else if (!lb)
        return lb;
    else
        return ans;
}


void smain() {
    int n;
    cin >> n;

    vi kek(n + 1);
    for (int i = 0; i <= n; ++i)
        cin >> kek[i];


    int l = -1, r = n + 1;
    while (r - l > 1) {
        int m = l + r >> 1;
        if (check(m, kek))
            r = m;
        else
            l = m;
    }


    if (r != n + 1)
    {
        int lb = 0, rb = 1e13 + 1;
//        int lb = 0, rb = 100;
        while (rb - lb > 1)
        {
            int m = lb + rb >> 1;
            if (check(r, kek, 1, m))
                lb = m;
            else
                rb = m;
        }

        cout << check(r, kek, 1, lb);
    }
    else
        cout << "-1\n";
}



Measured memory_bytes: 4056