#include <bits/stdc++.h>

#define ff first
#define ss second
#define pb push_back

using namespace std;
using ll = long long;
using ii = pair<int, int>;

const int N = 1005;
const int mod = 1e9+7;

int cnt[22];
int n, k, a[22];
int dp[22][N];
ll comb[N][N];

ll C(int x, int y){
	if(!x || !y || x == y) return 1;
	if(comb[x][y]) return comb[x][y];
	return comb[x][y] = (C(x-1, y) + C(x-1, y-1)) % mod;
}

int mul(ll aa, ll b){
	return int(aa * b % mod);
}

int add(int aa, int b){
	return (aa + b) % mod;
}

int f(int d, int q){
	if(q < 0) return 0;
	if(d == k) return q == 0;
	int &ret = dp[d][q];
	if(~ret) return ret;
	ret = 0;
	for(int i = 0; i <= a[d]; i++){
		ret += mul(mul(f(d+1, q - i), C(q, i)), C(n - i, a[d] - i));
		ret %= mod;
	}
	return ret;
}

int main() {
	scanf("%d %d", &n, &k);
	int sum = 0;
	for(int i = 0; i < k; i++){
		scanf("%d", a+i);
		sum += a[i];
	}
	memset(dp, -1, sizeof dp);
	printf("%d\n", f(0, n));
	return 0;
}
