#include<bits/stdc++.h>
#define mod 1000000007
using namespace std;
int n,k,a[21];
int dp[21][1005];
int C[1005][1005];

int main(){
	cin>>n>>k;
	for(int i=1;i<=k;i++) cin>>a[i];
	C[0][0]=1;
	for(int i=1;i<=n;i++){
		C[i][0]=1;
		for(int j=1;j<=i;j++) C[i][j]=(C[i-1][j-1]+C[i-1][j])%mod;
	}
	dp[0][0]=1;
	for(int i=1;i<=k;i++){
		for(int j=0;j<=n;j++){
			if(!dp[i-1][j]) continue;
			for(int l=0;l<=n-j&&l<=a[i];l++){
				(dp[i][j+l]+=1ll*C[n-j][l]*C[n-l][a[i]-l]%mod*dp[i-1][j]%mod)%=mod;
			}
		}
	}
	printf("%d\n",dp[k][n]);

	return 0;
}
