#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;

int N;
vector<int> nums;

const int conversion[2][2][2] = {{{0, 1}, {1, 1}}, {{0, 1}, {1, 0}}};

long dp[2000][2][2][2][2];

long choose(int now, int back_back, int back, int first, int second){
    if(now == N){
        return conversion[back_back][back][first] == nums[N - 1] && conversion[back][first][second] == nums[0];
    }else if(dp[now][back_back][back][first][second] != -1){
        return dp[now][back_back][back][first][second];
    }else{
        return dp[now][back_back][back][first][second] = (choose(now + 1, back, 0, first, second) * (conversion[back_back][back][0] == nums[now - 1]) +
                                                          choose(now + 1, back, 1, first, second) * (conversion[back_back][back][1] == nums[now - 1])) % int(1e9 + 7);
    }
}

int main(){
    cin >> N;
    nums.resize(N);
    for(int i = 0; i < N; i++){
        cin >> nums[i];
    }
    for(int i = 0; i < 2000; i++){
        for(int j = 0; j < 16; j++){
            dp[i][j & 1][(j >> 1) & 1][(j >> 2) & 1][(j >> 3) & 1] = -1;
        }
    }
    cout << (choose(2, 0, 0, 0, 0) + choose(2, 0, 1, 0, 1) + choose(2, 1, 0, 1, 0) + choose(2, 1, 1, 1, 1)) % int(1e9 + 7) << endl;
}