#include<bits/stdc++.h>
#define ll long long
#define ull unsigned ll
#define uint unsigned
#define pii pair<int,int>
#define pll pair<ll,ll>
#define IT iterator
#define PB push_back
#define fi first
#define se second
#define For(i,j,k) for (int i=(int)(j);i<=(int)(k);i++)
#define Rep(i,j,k) for (int i=(int)(j);i>=(int)(k);i--)
#define CLR(a,v) memset(a,v,sizeof(a));
#define CPY(a,b) memcpy(a,b,sizeof(a));
#define debug puts("wzpakking")
#define y1 ysghysgsygsh
using namespace std;
const int mo=1000000007;
const int N=1005;
int n,K,a[N];
int f[55][N],C[N][N];
int main(){
	scanf("%d%d",&n,&K);
	For(i,1,K) scanf("%d",&a[i]);
	For(i,0,n) C[i][0]=1;
	For(i,1,n) For(j,1,i)
		C[i][j]=(C[i-1][j]+C[i-1][j-1])%mo;
	f[0][0]=1;
	For(i,1,K) For(j,0,n) For(k,0,n-j)
		if (k<=a[i]) f[i][j+k]=(f[i][j+k]+1ll*f[i-1][j]*C[n-j][k]%mo*C[n-k][a[i]-k])%mo;
	//For(i,1,K) For(j,0,n) printf("%d %d %d\n",i,j,f[i][j]);
	printf("%d\n",f[K][n]);
}