#include <bits/stdc++.h>
using namespace std;
 
#define ll long long
#define all(aaa) aaa.begin(), aaa.end()

const int N = 1005, K = 21, MOD = 1e9 + 7;
int c[N][N];
ll dp[K][N];

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    int n, k;
    cin >> n >> k;

    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] = (c[i - 1][j] + c[i - 1][j - 1]) % MOD;
        }
    }

    dp[0][0] = 1;

    for (int i = 0; i < k; i++) {
        int x;
        cin >> x;

        for (int j = 0; j <= n; j++) {
            if (dp[i][j]) {
                for (int h = 0; h <= min(x, n - j); h++) {
                    dp[i + 1][j + h] = (dp[i + 1][j + h] 
                        + dp[i][j] * c[n - j][h] % MOD * c[n - h][x - h]) % MOD;
                }
            }
        }
    }

    cout << dp[k][n] << "\n";

    return 0;
}