#include<bits/stdc++.h>
using namespace std;
const int N = 1000010, mod = 1e9 + 7;
int f[5010], P[N], h[5010];
int main() {
	int n, k;
	scanf("%d%d", &n, &k);
	P[0] = 1;
	for(int i = 1; i <= n; i++)
		P[i] = 1ll * i * P[i - 1] % mod;
	for(int i = 1; i <= k; i++) {
		scanf("%d", h + i);
		n -= h[i];
	}
	f[k + 1] = P[n];
	for(int i = k; i >= 1; i--) {
		int sum = 0;
		for(int j = i; j <= k; j++) {
			sum += h[j];
			f[i] = (f[i] + P[sum] * f[j + 1]) % mod;
		}
		f[i] = (P[sum + n] - f[i] + mod) % mod;
	}
	printf("%d\n", f[1]);
	return 0;
}