#include <bits/stdc++.h>
#define rep(i,l,r) for (int i=l,i##end=r;i<=i##end;++i)
#define ll long long
using namespace std;
const int N=1003,P=1e9+7;
int C[N][N],f[N][N];
int add(int x,int y){ x+=y; return x>=P?x-P:x; }
int main(){
    int n,k; cin>>n>>k;
    rep(i,0,n){ C[i][0]=1; rep(j,1,i) C[i][j]=add(C[i-1][j],C[i-1][j-1]); }
    f[0][0]=1;
    rep(c,1,k){
        int a; cin>>a;
        rep(i,0,n)
            rep(j,0,min(i,a))
                f[c][i]=add(f[c][i],(ll)f[c-1][i-j]*C[n-(i-j)][j]%P*C[n-j][a-j]%P);
    }
    cout<<f[k][n]<<endl;
    return 0;
}
/*
4
1
*/
