#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<cstring>
#include<algorithm>
#define ll long long
#define inf 0x3f3f3f3f
#define mod 1000000007
#define maxn 2010
inline ll read()
{
	ll x=0; char c=getchar(),f=1;
	for(;c<'0'||'9'<c;c=getchar())if(c=='-')f=-1;
	for(;'0'<=c&&c<='9';c=getchar())x=x*10+c-'0';
	return x*f;
}
inline void write(ll x)
{
	static char buf[20];
	int len=0;
	if(x<0)putchar('-'),x=-x;
	for(;x;x/=10)buf[len++]=x%10+'0';
	if(!len)putchar('0');
	else while(len)putchar(buf[--len]);
}
inline void writesp(ll x){write(x); putchar(' ');}
inline void writeln(ll x){write(x); putchar('\n');}
ll fac[maxn],inv[maxn];
int f[maxn][maxn];
int a[maxn];
int n,m;
ll power(ll a,ll b)
{
	ll ans=1;
	for(;b;b>>=1,a=a*a%mod)
		if(b&1)ans=ans*a%mod;
	return ans;
}
ll C(int n,int m){return fac[n]*inv[m]%mod*inv[n-m]%mod;}
int main()
{
	n=read(); m=read();
	for(int i=1;i<=m;i++)
		a[i]=read();
	fac[0]=inv[0]=1;
	for(int i=1;i<=n;i++){
		fac[i]=fac[i-1]*i%mod;
		inv[i]=power(fac[i],mod-2);
	}
	f[0][0]=1;
	for(int i=1;i<=m;i++)
		for(int j=n;j>=0;j--){
			f[i][j]=0;
			for(int k=0;k<=a[i]&&k<=j;k++)
				f[i][j]=(f[i][j]+C(n-k,a[i]-k)*inv[k]%mod*f[i-1][j-k])%mod;
		}
	writeln(f[m][n]*fac[n]%mod);
	return 0;
}