#include <bits/stdc++.h>

using namespace std;

const long long MOD = 1e9 + 7;

long long dp[2000][1<<3][1<<2];

bool check(int x, int mask) {
  if (mask == 7) return x == 0;
  if (!(mask & 3)) return x == 0;
  return x == 1;
}

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

  int n;
  cin >> n;
  vector<int> a(n);
  for (int i = 0; i < n; i++)
    cin >> a[i];

  for (int mask = 0; mask < 1<<3; mask++) {
    if (check(a[1], mask))
        dp[0][mask][mask>>1] = 1;
  }

  for (int i = 1; i + 2 < n; i++) {
    for (int mask = 0; mask < 1<<3; mask++) {
      if (!check(a[i+1], mask)) continue;
      for (int j = 0; j < 1<<2; j++) {
        int n1 = mask >> 1;
        int n2 = n1 | (1 << 2);
        dp[i][mask][j] = (dp[i-1][n1][j] + dp[i-1][n2][j]) % MOD;
      }
    }
  }

  long long ret = 0;
  for (int mask = 0; mask < 1<<3; mask++) {
    for (int j = 0; j < 1<<2; j++) {
      int n1 = ((mask & 3) << 1) | (j >> 1);
      int n2 = ((mask & 1) << 2) | j;
      if (check(a[n-1], n1) && check(a[0], n2)) {
        ret += dp[n-3][mask][j];
        ret %= MOD;
      }
    }
  }
  cout << ret << endl;

  return 0;
}