#include<cstring>
#include<algorithm>
#include<cstdio>
#define rep(a,b,c) for (int a=b;a<=c;a++)
#define per(a,b,c) for (int a=b;a>=c;a--)
typedef long long LL;
typedef double dob;
using namespace std;
const int P=1000000007;
const int N=1010;
int c[N][N],f[N],g[N],n,k,a[N];
void upd(int &x,int y){x=(x+y)%P;}
int C(int x,int y){return c[x][y];}
int main(){
	scanf("%d%d",&n,&k);
	rep(i,1,k) scanf("%d",a+i);
	f[0]=1;
	rep(i,0,1000) c[i][i]=c[i][0]=1;
	rep(i,1,1000) rep(j,1,i-1) c[i][j]=(c[i-1][j-1]+c[i-1][j])%P;
	rep(i,1,k){
		memset(g,0,sizeof(g));
		rep(j,0,n) if (f[j]){
			rep(t,0,min(a[i],n-j)){
				upd(g[j+t],(LL)f[j]*C(n-j,t)%P*C(n-t,a[i]-t)%P);
			}
		}
		swap(f,g);
	}
	f[n]=(f[n]%P+P)%P;
	printf("%d\n",f[n]); 
	return 0;
}
