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

using ll = long long;

#define N 1005

int n, k, a[30];

const int mod = 1e9 + 7;

int dp[2][N];

void add(int &x, int y) {
	x += y;
	if (x >= mod) x -= mod;
}
int mul(int x, int y) {
	return 1ll * x * y % mod;
}

int inv[N] = {0, 1}, fac[N] = {1, 1};

void init() {
	for (int i = 2; i < N; i ++) {
		inv[i] = 1ll * (mod / i) * (mod - inv[mod % i]) % mod;
		fac[i] = 1ll * fac[i-1] * inv[i] % mod;
	}
	return;
}

int C[N][N];

int main() {
	int u = 0, v = 1;
	dp[0][0] = 1;
	cin >> n >> k;
	init();
	for (int i = 1; i <= k; i ++) cin >> a[i];
	C[0][0] = 1;
	for (int i = 1; i < N; i ++) {
		C[i][0] = 1;
		for (int j = 1; j <= i; j ++) {
			add(C[i][j], C[i-1][j]);
			add(C[i][j], C[i-1][j-1]);
		}
	}
	for (int i = 1; i <= k; i ++) {
		memset(dp[v], 0, sizeof dp[v]);
		int mx = a[i];
		for (int j = 0; j <= mx; j ++) {
			for (int p = 0; p <= n; p ++) if (p + j <= n) {
				add(dp[v][p+j], mul(mul(C[n-j][mx-j], fac[j]), dp[u][p]));
			}
		}
		swap(u, v);
	}
	int ans = dp[u][n];
	for (int i = 1; i <= n; i ++) ans = mul(ans, i);
	cout << ans << endl;
	return 0;
}
