#include <bits/stdc++.h>

using namespace std;
using ll = long long int;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vi = vector<int>;
using vl = vector<ll>;
using vb = vector<bool>;
using vs = vector<string>;
using vvi = vector<vector<int>>;
using vvl = vector<vector<ll>>;
using vvb = vector<vector<bool>>;
using vvs = vector<vector<string>>;
template<typename T> using vv = vector<vector<T>>;
template<typename T> using vvv = vector<vector<vector<T>>>;
template<typename T> using pq = priority_queue<T>;
template<typename T> using pqg = priority_queue<T, vector<T>, greater<T>>;

const int INF = 1e9;
const ll LINF = 1e18;
const ll MOD = 1e9 + 7;
const int DX[4] = {1, 0, -1, 0};
const int DY[4] = {0, 1, 0, -1};

#define _sel(_1, _2, x, ...) x
#define repn(i, n) for (ll i = 0; i < (n); i++)
#define reps(i, a, b) for (ll i = (a); i < (b); i++)
#define rep(i, ...) _sel(__VA_ARGS__, reps, repn)(i, __VA_ARGS__)
#define reppn(i, n) for (ll i = 1; i <= (n); i++)
#define repps(i, a, b) for (ll i = (a); i <= (b); i++)
#define repp(i, ...) _sel(__VA_ARGS__, repps, reppn)(i, __VA_ARGS__)
#define rrepn(i, n) for (ll i = (n) - 1; i >= 0; i--)
#define rreps(i, a, b) for (ll i = (b) - 1; i >= (a); i--)
#define rrep(i, ...) _sel(__VA_ARGS__, rreps, rrepn)(i, __VA_ARGS__)
#define rreppn(i, n) for (ll i = (n); i >= 1; i--)
#define rrepps(i, a, b) for (ll i = (b); i >= (a); i--)
#define rrepp(i, ...) _sel(__VA_ARGS__, rrepps, rreppn)(i, __VA_ARGS__)

#define pb push_back
#define mp make_pair
#define mt make_tuple
#define fi first
#define se second
#define rng(v) (v).begin(), (v).end()
#define rrng(v) (v).rbegin(), (v).rend()
#define siz(x) int((x).size())
#define pow2(x) (1ll << (x))
#define bit(x, n) ((x) >> (n) & 1)
#define prt(x) cout << (x) << endl
#define dbg(x) dbgn(#x, x)

template<typename T, typename U> inline bool umax(T& m, U x) { if (m < x) { m = x; return true; } return false; }
template<typename T, typename U> inline bool umin(T& m, U x) { if (m > x) { m = x; return true; } return false; }
template<typename T> inline void errv(T& v) { for (auto x: v) cerr << x << " "; cerr << endl; }
inline void errv(vb& v) { for (auto x: v) cerr << (x ? 1 : 0) << " "; cerr << endl; }
template<typename T> inline void dbgn(string n, T x) { cerr << n << ": " << x << endl; }
template<typename T> inline void dbgn(string n, vector<T>& v) { cerr << n << ": "; errv(v); }
template<typename T> inline void dbgn(string n, vv<T>& m) { cerr << n << ":" << endl; for (auto& v: m) errv(v); }


int main() {
    int n; cin >> n;
    vl a(n + 1);
    rep(i, n + 1) cin >> a[i];

    vector<pll> rg(n + 2);
    rg[n + 1] = mp(0, 0);
    rrep(i, n + 1) {
        rg[i].fi = rg[i + 1].fi + a[i];
        if (rg[i].fi > pow2(i <= 60 ? i : 60)) {
            prt(-1);
            return 0;
        }
        rg[i].se = rg[i + 1].se + a[i];
        rg[i].fi = (rg[i].fi + 1) / 2;
    }

    if (rg[0].fi > 1) {
        prt(-1);
        return 0;
    }

    ll ans = 0;
    ll r = 1;
    rep(i, n + 1) {
        if (r < rg[i].fi) {
            prt(-1);
            return 0;
        }
        ll t = min(r, rg[i].se);
        ans += t;
        r = min((t - a[i]) * 2, LINF);
    }

    prt(ans);

    return 0;
}


Measured memory_bytes: 5592