#include <iostream>
#include <cstdio>
#include <vector>
#include <cstring>
#include <algorithm>
using namespace std;
const int N = 1e5 + 5;
const int mod = 1e9 + 7;

int fpow(int a, int b, int p) {
	if (b == 0)
		return 1;
	int ans = fpow(a, b / 2, p);
	ans = 1ll * ans * ans % p;
	if (b % 2 == 1)
		ans = 1ll * a * ans % p;
	return ans; 
}

int fac[N] = {0}, inv[N] = {0};
void init(int n) {
	fac[0] = 1;
	for (int i = 1; i <= n; i++)
		fac[i] = 1ll * i * fac[i - 1] % mod;
	inv[n] = fpow(fac[n], mod - 2, mod);
	for (int i = n - 1; i >= 0; i--)
		inv[i] = 1ll * (i + 1) * inv[i + 1] % mod;
}
int cmb(int n, int m) {
	if (n < m)
		return 0;
	return 1ll * fac[n] * inv[m] % mod * inv[n - m] % mod;
}

int main() {
	int n;
	cin >> n;
	init(n);
	int ans = fac[n - 2];
	int tot = 0;
	for (int i = 1, x; i <= n; i++)
		cin >> x, ans = 1ll * ans * inv[x - 1] % mod, tot += (x - 1);
	if (tot != n - 2)
		ans = 0;
	cout << ans << endl;
	return 0;
}