#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <stack>
#include <queue>
#include <cmath>
#include <tuple>
#include <cstdio>
#include <bitset>
#include <sstream>
#include <iterator>
#include <numeric>
#include <map>
#include <cstring>
#include <set>

using namespace std;

#define DEBUG_ //!!提出時にコメントアウト!!
#ifdef DEBUG_
	#define dump(x)  cerr << #x << " = " << (x) << endl;
#else
	#define dump(x)  ; //何もしない文
#endif

#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)
#define SZ(x) ((int)(x).size()) //unsignedのサイズをint型に変換
#define pb push_back

//#define int long long

typedef long long LL;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef pair<LL, LL> PLL;

template <typename T>
std::string printVector(const std::vector<T> &data)
{
    std::stringstream ss;
    std::ostream_iterator<T> out_it(ss, ", ");
    ss << "[";
    std::copy(data.begin(), data.end() - 1, out_it);
    ss << data.back() << "]";
    return ss.str();
}

const int MOD = 1e9+7;
const LL LINF = 1001002003004005006ll;
const int INF = 1001001001;


LL dp[2020][2][2];
int e[2020];
int N;

int f(int a, int b, int c)
{
    if(a == 1 && b == 1 && c == 1) return 0;
    if(b == 0 && c == 0) return 0;
    return 1;
}

LL solve(int v0, int v1)
{
    REP(i,2020) REP(j,2) REP(k,2) dp[i][j][k] = 0;
    dp[2][v0][v1] = 1;
    FOR(i,2,N) FOR(a,0,2) FOR(b,0,2) FOR(c,0,2)
    {
        if(f(a,b,c) == e[i-1])
        {
            dp[i+1][b][c] += dp[i][a][b];
        }
    }
    LL ans = 0;
    FOR(a,0,2) FOR(b,0,2)
    {
        if(f(a,b,v0) == e[N-1] && f(b,v0,v1) == e[0]) ans += dp[N][a][b];
    }
    return ans;
}

signed main(int argc, char const *argv[])
{
    cin.tie(0);
    ios::sync_with_stdio(false);

    cin >> N;
    REP(i,N) cin >> e[i];
    LL ans = 0;
    FOR(v0,0,2) FOR(v1,0,2) ans += solve(v0,v1);
    cout << ans % MOD << endl;



}