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

const int N = 1005, K = 25;
const long long mod = 1000000007ll;

int n, k, a[K];
long long c[N][N], f[N][K];
int main () {
	cin >> n >> k;
	for (int i = 1; i <= k; i++) cin >> a[i];

	for (int i = 0; i <= n; i++) c[i][i] = c[i][0] = 1ll;
	for (int i = 1; i <= n; i++) {
		for (int j = 1; j < i; j++) c[i][j] = (c[i - 1][j] + c[i - 1][j - 1]) % mod;
	}

	for (int i = 1; i <= n; i++) f[i][0] = 0ll;
	f[0][0] = 1ll;

	for (int i = 1; i <= k; i++) {
		for (int j = 0; j <= n; j++) {
			f[j][i] = 0ll;
			for (int j_ = 0; j_ <= min(j, a[i]); j_++) {
				f[j][i] = (f[j][i] + f[j - j_][i - 1] * c[j][j_] % mod * c[n - j_][a[i] - j_]) % mod;
			}
		}
	}
	printf("%lld\n", f[n][k]);
	return 0;
}