#include <bits/stdc++.h>

using namespace std;

const long long MOD = 1e9 + 7;
long long comb[32][32];

void init() {
  for (int i = 0; i < 32; i++) {
    comb[i][0] = comb[i][i] = 1;
    for (int j = 1; j < i; j++)
      comb[i][j] = (comb[i-1][j-1] + comb[i-1][j]) % MOD;
  }
}

long long modpow(long long x, long long p, long long mod) {
  long long ret = 1;
  while (p) {
    if (p & 1)
      ret = ret * x % mod;
    x = x * x % mod;
    p >>= 1;
  }
  return ret;
}

long long calc(int x, int y, int n) {

  vector<long long> cur(32);
  cur[x] = 1;
  
  for (int i = 0; i < n; i++) {
    vector<long long> nxt(32);

    // xで立っているbitがall zeroのとき
    for (int j = x; j <= y; j++) {
      for (int k = 1; k <= y-j; k++) {
        nxt[j+k] += cur[j] * comb[y-j][k] % MOD;
        nxt[j+k] %= MOD;
      }
    }

    // xで立っているbitがall zeroではないとき
    for (int j = x; j <= y; j++) {
      long long base = modpow(2, j, MOD) - 1;
      if (base < 0)
        base += MOD;
      base = base * cur[j] % MOD;
      for (int k = 0; k <= y-j; k++) {
        nxt[j+k] += base * comb[y-j][k] % MOD;
        nxt[j+k] %= MOD;
      }
    }
    cur = nxt;
  }

  return cur[y];
}

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  init();
  
  int n;
  cin >> n;
  vector<int> b(n);
  vector<int> p;

  for (int i = 0; i < n; i++) {
    cin >> b[i];
    if (b[i] != -1)
      p.push_back(i);
  }

  long long ret = 1;
  int j = -1;
  int x = 0;
  for (int i: p) {
    int y = b[i];
    if ((y & x) != x) {
      ret = 0;
      break;
    }

    int bx = __builtin_popcountll(x);
    int by = __builtin_popcountll(y);

    ret *= calc(bx, by, i-j);
    ret %= MOD;

    x = y;
    j = i;
  }

  cout << ret << endl;
  
  return 0;
}