#include <bits/stdc++.h>
using namespace std;
#define ri register int
const int N=1e3+5,K=25,mod=1e9+7;
int a[N],f[K][N],c[N][N]; 
inline int _add(ri x,ri y){
	return (x+=y)>=mod?x-mod:x;
}
int main(){
	ri n,k,i,j,x;
	scanf("%d%d",&n,&k);
	for(i=1;i<=k;++i) scanf("%d",&a[i]);
	for(i=0;i<=n;++i){
		c[i][0]=1;
		for(j=1;j<=i;++j)
			c[i][j]=_add(c[i-1][j],c[i-1][j-1]);
	//	for(j=0;j<=i;++j)
	//		printf("%d ",c[i][j]);
	//	puts("");
	}
	f[0][0]=1;
	for(i=1;i<=k;++i)
		for(j=0;j<=n;++j)
			for(x=0;x<=j&&x<=a[i];++x)
				f[i][j]=(f[i][j]+(long long)f[i-1][j-x]*c[n-(j-x)][x]%mod*c[n-x][a[i]-x])%mod;
	printf("%d\n",f[k][n]);
	return 0;
}