#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <utility>

using namespace std;

const long long MOD = 1e9 + 7;

int main() {
	int m, x;

	cin >> m;
	vector<int> h(m);

	int blocks = 0;
	int total = 0;
	while (cin >> x) {
		total += x;
		blocks++;
	}

	int rest = m - total - (blocks - 1);
	// printf("%d %d %d\n", rest, blocks, total);

	if (rest < 0) {
		cout << "NA" << endl;
		return 0;
	} else if (total == 0) {
		cout << 1 << endl;
		return 0;
	}

	//(blocks + rest)C(rest)
	long long ans = 1;
	for (long long i = blocks + rest; i > 1; i--) {
		ans = ans * i % MOD;
	}

	long long denominator = 1;
	for (long long i = blocks; i > 1; i--) {
		denominator = denominator * i % MOD;
	}
	for (long long i = rest; i > 1; i--) {
		denominator = denominator * i % MOD;
	}

	vector<long long> pows(31, 1);
	pows[1] = denominator;
	for (int i = 2; i < pows.size(); i++) {
		pows[i] = pows[i - 1] * pows[i - 1] % MOD;
	}
	int p2 = MOD - 2;

	long long inv_denom = 1;
	for (int i = 31; i >= 0; i--) {
		if ((p2 >> i) & 1) {
			inv_denom = inv_denom * pows[i] % MOD;
		}
	}
	// printf("ans %lld\n", ans);
	// printf("denom %lld\n", denominator);
	// printf("inv %lld\n", inv_denom);

	ans = ans * inv_denom % MOD;

	cout << ans << endl;

	return 0;
}