UVa 10105 - Polynomial Coefficients

// UVa 10105 - Polynomial Coefficients
#include <iostream>
using namespace std;

#define integer unsigned long long

int main() {
	integer f[13];
	f[0] = 1;
	for (int i = 1; i < 13; i++)
		f[i] = f[i - 1] * i;
	int n, k;
	while (cin >> n >> k) {
		integer den = 1;
		for (int i = 0; i < k; i++) {
			int nk;
			cin >> nk;
			den *= f[nk];
		}
		cout << f[n] / den << endl;
	}
	return 0;
}