#include <bits/stdc++.h>
using namespace std;

const int M = 1e9 + 7;

int dp(const vector<int> &e, int a, int b) {
  auto f = [&](int x, int y, int z) {
    return !(!y & !z | x & y & z);
  };
  vector<vector<vector<int>>> d(2001, vector<vector<int>>(2, vector<int>(2)));
  d[2][a][b] = 1;
  for (int i = 2; i < e.size(); ++i) {
    for (int x = 0; x < 2; ++x) {
      for (int y = 0; y < 2; ++y) {
        for (int z = 0; z < 2; ++z) {
          if (f(x, y, z) == e[i]) {
            (d[i + 1][y][z] += d[i][x][y]) %= M;
          }
        }
      }
    }
  }
  int r = 0;
  for (int i = 0; i < 2; ++i) {
    for (int j = 0; j < 2; ++j) {
      if (f(i, j, a) == e[0] && f(j, a, b) == e[1]) {
        (r += d[e.size()][i][j]) %= M;
      }
    }
  }
  return r;
}

signed main() {
  ios::sync_with_stdio(false);
  int N;
  cin >> N;
  vector<int> E(N);
  for (int i = 0; i < N; ++i) {
    cin >> E[i];
  }
  int ans = 0;
  for (int i = 0; i < 2; ++i) {
    for (int j = 0; j < 2; ++j) {
      (ans += dp(E, i, j)) %= M;
    }
  }
  cout << ans << endl;
  return 0;
}