using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var n = NN;
        var b = new int[n];
        for (var i = 0; i < n; ++i) b[i] = NN;
        WriteLine((Calc(n, b, 0, 0) + Calc(n, b, 0, 1) + Calc(n, b, 1, 0) + Calc(n, b, 1, 1)) % mod); 
    }
    static int mod = 1_000_000_007;
    static long Calc(int n, int[] b, int left, int right)
    {
        if (left == 0 && right == 0 && b[0] == 1) return 0;
        var dp = new long[n, 4];
        if (b[0] == 0)
        {
            if (left == 0 && right == 0)
            {
                dp[0, 0] = 1;
                dp[0, 1] = 1;
            }
            else if (left == 1 && right == 1)
            {
                dp[0, 3] = 1;
            }
        }
        else
        {
            if (left == 0 && right == 1)
            {
                dp[0, 0] = 1;
                dp[0, 1] = 1;
            }
            else if (left == 1 && right == 0)
            {
                dp[0, 2] = 1;
                dp[0, 3] = 1;
            }
            else if (left == 1 && right == 1)
            {
                dp[0, 2] = 1;
            }
        }
        for (var i = 1; i < n; ++i)
        {
            if (b[i] == 0)
            {
                dp[i, 0] = dp[i - 1, 0];
                dp[i, 1] = dp[i - 1, 0];
                dp[i, 3] = dp[i - 1, 3];
            }
            else
            {
                dp[i, 0] = dp[i - 1, 2];
                dp[i, 1] = dp[i - 1, 2];
                dp[i, 2] = (dp[i - 1, 1] + dp[i - 1, 3]) % mod;
                dp[i, 3] = dp[i - 1, 1];
            }
        }
        if (right == 0 && left == 0) return dp[n - 1, 0];
        if (right == 0 && left == 1) return dp[n - 1, 1];
        if (right == 1 && left == 0) return dp[n - 1, 2];
        return dp[n - 1, 3];
    }
}