#include <bits/stdc++.h>
using namespace std;
#define F first
#define S second
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<pii> vpii;
typedef vector<pll> vpll;

ll MOD=1e9+7;

ll modinv(ll x)
{
    ll res=1;
    ll pw=MOD-2;
    while(pw>0)
    {
        if(pw%2) res=(res*x)%MOD;
        pw/=2;
        x=(x*x)%MOD;
    }
    return res;
}
ll n, k;

ll ch[1009][1009];
ll a[1009];
ll dp[29][1009];

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cin>>n>>k;
    for(int i=1; i<=k; i++) cin>>a[i];
    for(int i=0; i<=1000; i++)
    {
        ch[i][0]=1;
        ch[i][i]=1;
    }
    for(int i=1; i<=1000; i++)
    {
        for(int j=1; j<i; j++)
        {
            ch[i][j]=(ch[i-1][j-1]+ch[i-1][j])%MOD;
        }
    }
    for(int i=0; i<=n; i++)
    {
        if(i<=a[1]) dp[1][i]=(ch[a[1]][i]*ch[n][a[1]])%MOD;
        else dp[1][i]=0;
        //cout<<"dp i="<<1<<" db="<<i<<" ::: "<<dp[1][i]<<endl;
    }
    for(int i=2; i<=k; i++)
    {
        for(ll db=0; db<=n; db++)
        {
            for(ll akt=0; akt<=min(db, a[i]); akt++)
            {
                //ll pl=ch[a[i]][akt];
                ll pl=1LL;
                if(n-(db-akt)<akt) continue;
                pl=(pl*ch[n-(db-akt)][akt])%MOD;
                pl=(pl*ch[n-akt][a[i]-akt])%MOD;
                pl=(pl*dp[i-1][db-akt])%MOD;
                //cout<<"plusz ("<<akt<<") "<<pl<<endl;
                dp[i][db]=(dp[i][db]+pl)%MOD;
            }
            //cout<<"dp i="<<i<<" db="<<db<<" ::: "<<dp[i][db]<<endl;
        }
    }
    ll ans=dp[k][n];
    /*for(int i=1; i<=n; i++)
    {
        ans=(ans*ch[n][a[i]])%MOD;
    }*/
    cout<<ans<<endl;
    return 0;
}
