#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using VI = vector<int>;
using VL = vector<ll>;
using VS = vector<string>;
template<class T> using PQ = priority_queue<T, vector<T>, greater<T>>;
using graph = vector<VI>;
template<class T = ll> using w_graph = vector<vector<pair<int, T>>>;
#define FOR(i,a,n) for(int i=(a);i<(n);++i)
#define eFOR(i,a,n) for(int i=(a);i<=(n);++i)
#define rFOR(i,a,n) for(int i=(n)-1;i>=(a);--i)
#define erFOR(i,a,n) for(int i=(n);i>=(a);--i)
#define SORT(a) sort(a.begin(),a.end())
#define rSORT(a) sort(a.rbegin(),a.rend())
#define fSORT(a,f) sort(a.begin(),a.end(),f)
#define all(a) a.begin(),a.end()
#define out(y,x) ((y)<0||h<=(y)||(x)<0||w<=(x))
#define tp(a,i) get<i>(a)
#ifdef _DEBUG
#define line cout << "-----------------------------\n"
#define stop system("pause")
#endif
constexpr ll INF = 1000000000;
constexpr ll LLINF = 1LL << 60;
constexpr ll mod = 1000000007;
constexpr ll MOD = 998244353;
constexpr ld eps = 1e-10;
constexpr ld pi = 3.1415926535897932;
template<class T>inline bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; }return false; }
template<class T>inline bool chmin(T& a, const T& b) { if (a > b) { a = b; return true; }return false; }
inline void init() { cin.tie(nullptr); cout.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(15); }
template<class T>inline istream& operator>>(istream& is, vector<T>& v) { for (auto& a : v)is >> a; return is; }
template<class T, class U>inline istream& operator>>(istream& is, pair<T, U>& p) { is >> p.first >> p.second; return is; }
template<class T>inline vector<T> vec(size_t a) { return vector<T>(a); }
template<class T>inline vector<T> defvec(T def, size_t a) { return vector<T>(a, def); }
template<class T, class... Ts>inline auto vec(size_t a, Ts... ts) { return vector<decltype(vec<T>(ts...))>(a, vec<T>(ts...)); }
template<class T, class... Ts>inline auto defvec(T def, size_t a, Ts... ts) { return vector<decltype(defvec<T>(def, ts...))>(a, defvec<T>(def, ts...)); }
template<class T>inline void print(const T& a) { cout << a << "\n"; }
template<class T, class... Ts>inline void print(const T& a, const Ts&... ts) { cout << a << " "; print(ts...); }
template<class T>inline void print(const vector<T>& v) { for (int i = 0; i < v.size(); ++i)cout << v[i] << (i == v.size() - 1 ? "\n" : " "); }
template<class T>inline void print(const vector<vector<T>>& v) { for (auto& a : v)print(a); }
inline string reversed(const string& s) { string t = s; reverse(all(t)); return t; }
template<class T>inline T sum(const vector<T>& a, int l, int r) { return a[r] - (l == 0 ? 0 : a[l - 1]); }
template<class T>inline void END(T s) { print(s); exit(0); }
void END() { exit(0); }

#include <atcoder/all>
using namespace atcoder;
using mint = modint1000000007;
class combination {
    int n;
    ll c_mod;
    VL fac, finv, inv;
public:
    combination(int n, ll c_mod) : n(n), c_mod(c_mod), fac(n), finv(n), inv(n) {
        fac[0] = fac[1] = 1;
        finv[0] = finv[1] = 1;
        inv[1] = 1;
        FOR(i, 2, n) {
            fac[i] = fac[i - 1] * i % c_mod;
            inv[i] = c_mod - inv[c_mod % i] * (c_mod / i) % c_mod;
            finv[i] = finv[i - 1] * inv[i] % c_mod;
        }
    }
    ll operator()(int n, int k) {
        if (n < k) return 0;
        if (n < 0 || k < 0) return 0;
        return fac[n] * (finv[k] * finv[n - k] % c_mod) % c_mod;
    }
};

int main() {
    init();

    int n; cin >> n;
    VI b(n); cin >> b;

    combination com(n + 1, mod);

    mint ans = 1;
    int pre = 0;
    FOR(i, 0, n) {
        int d = 1;
        for (; b[i] == -1; ++d, ++i);
        mint cur = 0;
        eFOR(k, 0, d) {
            mint s = com(d, k);
            int rem = d - k;
            FOR(j, 0, 30) {
                bool x = pre >> j & 1, y = b[i] >> j & 1;
                if (x) {
                    if (y) {
                        s *= pow_mod(2, rem, mod);
                    }
                    else {
                        s = 0;
                    }
                }
                else {
                    if (y) {
                        if (rem == 0) {
                            s = 0;
                        }
                        else {
                            s *= pow_mod(2, rem, mod) - 1;
                        }
                    }
                }
            }
            if (k & 1)cur -= s;
            else cur += s;
        }
        ans *= cur;
        pre = b[i];
    }
    print(ans.val());

    return 0;
}