#include<bits/stdc++.h>
using namespace std;
#define int long long
#define ii pair <int, int>
#define app push_back
#define all(a) a.begin(), a.end()
#define bp __builtin_popcount
#define ll long long
#define mp make_pair
#define f first
#define s second
#define Time (double)clock()/CLOCKS_PER_SEC
const int N = 1007, K = 21, MOD = 1000 * 1000 * 1000 + 7;

int mod(int n) {
    n %= MOD;
    if (n < 0) return n + MOD;
    else return n;
}   
int fp(int a, int p) {
    int ans = 1, c = a;
    for (int i = 0; (1ll << i) <= p; ++i) {
        if ((p >> i) & 1) ans = mod(ans * c);
        c = mod(c * c);
    }   
    return ans;
}   
int dv(int a, int b) { return mod(a * fp(b, MOD - 2)); }
void add(int &a, int b) {
    a = mod(a + b);
}

int C[N][N];
int dp[K][N];
int a[K];
signed main() {
    #ifdef HOME
    freopen("input.txt", "r", stdin);
    #else
    ios_base::sync_with_stdio(0); cin.tie(0);
    #endif
    for (int i = 0; i < N; ++i) 
        C[i][0] = 1;
    for (int i = 1; i < N; ++i)
        for (int j = 1; j < N; ++j)
            C[i][j] = mod(C[i - 1][j - 1] + C[i - 1][j]);
    int n, k;
    cin >> n >> k;
    for (int i = 0; i < k; ++i)
        cin >> a[i];
    dp[0][0] = 1;
    for (int i = 0; i < k; ++i) 
        for (int j = 0; j <= n; ++j) 
            for (int t = 0; j + t <= n && t <= a[i]; ++t) 
                add(dp[i + 1][j + t], dp[i][j] * mod(C[n - j][t] * C[n - t][a[i] - t]));
    cout << dp[k][n] << '\n';
}   