#include<bits/stdc++.h>
using namespace std;
const int mod = 1e9 + 7;
const int N = 1e3 + 11;
int n, K;
int f[22][N], C[N][N], a[N];
inline int A(int x, int y){
    return x + y - (x + y >= mod ? mod : 0);
}
inline int M(int x, int y){
    return 1LL * x * y % mod;
}
int main(){
    C[0][0] = 1;
    for(int i = 1;i <= 1000; i++){
        C[i][0] = 1;
        for(int j = 1;j <= 1000; j++)
            C[i][j] = A(C[i-1][j], C[i-1][j-1]);
    }
    cin>>n>>K;
    for(int i = 1;i <= K; i++){
        cin>>a[i];
    }
    f[0][0] = 1;
    for(int i = 0;i < K; i++){
        for(int j = 0;j <= n; j++){
            for(int k = 0;j + k <= n; k++){
                if(k <= a[i+1])
                    f[i+1][j+k] = A(f[i+1][j+k], M(f[i][j], M(C[n-j][k], C[n-k][a[i+1]-k])));
            }
        }
    }
    cout<<f[K][n]<<endl;
    return 0;
}
