#include <bits/stdc++.h>

using namespace std;

// c++ short types
#define vt vector
//typedef long long ll;
typedef long double ld;

void whattime() { cout << "finished in " << clock() * 1.0 / CLOCKS_PER_SEC << " sec" << endl; }
const int inf = 1e9;
const int mod = 1e9+7;
bool debug = false;
const ld eps = 1e-9;

mt19937_64 rng((unsigned int) chrono::steady_clock::now().time_since_epoch().count());

void add(int &a, int b) {
	a += b;
	if(a >= mod) {
		a -= mod;
	}
	if(a < 0) {
		a += mod;
	}
}
int mul(int a, int b) {
	return a * 1ll * b % mod;
}
int bin_pow(int b, int p) {
	int r = 1;
	for(;p;p>>=1,b=mul(b,b)) {
		if(p&1) {
			r = mul(r, b);
		}
	}
	return r;
}
int inv(int x) {
	return bin_pow(x, mod-2);
}

void solve() {
	int n; cin >> n;
	vt<int> d(n);
	for(int i = 0; i < n; ++i) {
		cin >> d[i];
	}
	int fact = 1;
	for(int i = 1; i <= n-2; ++i) {
		fact = mul(fact, i);
	}
	int cnt = 0;
	for(int i = 0; i < n; ++i) {
		cnt += d[i];
	}
	if(cnt != 2 * n -2) {
		cout << 0 << "\n";
		return ;
	}
	for(int i = 0; i < n; ++i) {
		if(d[i] == 3) {
			fact = mul(fact, inv(2));
		}
	}
	cout << fact << '\n';
}

int main()
{
	ios::sync_with_stdio(false); cin.tie(nullptr);
	int tt = 1;
	if(debug) {
		tt = 1e5;
	} else {
//		cin >> tt;
	}
	for(int t = 0; t < tt; ++t) {
		solve();
	}
	return 0;
}