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

#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, a, b) for(int i = (a) - 1; i >= (b); i--)
#define SZ(a) int(a.size())
#define ALL(a) a.begin(), a.end()
#define PB push_back
#define MP make_pair
#define F first
#define S second

typedef long long LL;
typedef vector<int> VI;
typedef pair<int, int> PII;
typedef double db;

const int mod = 1'000'000'007;
const int inv2 = (mod + 1) / 2;

int mult(int a, int b)
{
	return (LL)a * b % mod;
}

int main()
{
	ios::sync_with_stdio(0); 
	cin.tie(0);
	int n;
	cin >> n;
	int ans = 1;
	FOR(i, 1, n - 1)
		ans = mult(ans, i);
	int c1 = 0, c2 = 0, c3 = 0;
	FOR(i, 0, n)
	{
		int a;
		cin >> a;
		if (a == 1)
			c1++;
		else if (a == 2)
			c2++;
		else if (a == 3)
		{
			c3++;
			ans = mult(ans, inv2);
		}
	}
	if (c1 + 2 * c2 + 3 * c3 != 2 * (n - 1))
	{
		cout << "0\n";
		return 0;
	}
	cout << ans << "\n";
	return 0;
}