#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define f(i, x, n) for (int i = x; i < (int)(n); ++i)

int const N = 1000, md = 1e9 + 7;
int dp[N + 1], ch[N + 1][N + 1];

void ad(int &x, int y) { if ((x += y) >= md)x -= md; }

int main(){
	int n, k;
	scanf("%d%d", &n, &k);
	f(i, 0, n + 1){
		ch[i][0] = 1;
		f(j, 1, i + 1)ad(ch[i][j] = ch[i - 1][j], ch[i - 1][j - 1]);
	}
	dp[0] = 1;
	f(it, 0, k){
		int a;
		scanf("%d", &a);
		for (int i = n; i >= 0; --i){
			dp[i] = (ll)dp[i] * ch[n][a] % md;
			f(j, max(0, i - a), i)ad(dp[i], (ll)dp[j] * ch[n - j][i - j] % md * ch[n - i + j][a - i + j] % md);
		}
	}
	printf("%d\n", dp[n]);
}