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

using int64 = long long;
using uint64 = unsigned long long;

const int64 MOD = 1e9 + 7;

const int MAX_N = 2000;
int N, e[MAX_N];
int64 dp[MAX_N + 2][2][2];

// a b c
// . d .
int nextState(int a, int b, int c)
{
    if ((a == 1 and b == 1 and c == 1) or (b == 0 and c == 0))
    {
        return 0;
    }
    else
    {
        return 1;
    }
}

int64 counting(int d0, int d1)
{
    memset(dp, 0, sizeof(dp));
    dp[1][d0][d1] = 1;

    for (int i = 1; i <= N; i++) for (int p : {0, 1})
    for (int c : {0, 1}) for (int nxt : {0, 1})
    {
        if (nextState(p, c, nxt) == e[i % N])
        {
            (dp[i + 1][c][nxt] += dp[i][p][c]) %= MOD;
        }
    }
    return dp[N + 1][d0][d1];
}

int main()
{
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    cin >> N;

    for (int i = 0; i < N; i++)
    {
        cin >> e[i];
    }

    int64 ans = 0;
    for (int d0 : {0, 1})
    {
        for (int d1 : {0, 1})
        {
            (ans += counting(d0, d1)) %= MOD;
        }
    }
    cout << ans << endl;

    return 0;
}