#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  ;
  long long int n, k;
  cin >> n >> k;
  long long int dp[k + 2][n + 2];
  memset(dp, 0, sizeof(dp));
  dp[0][0] = 1;
  long long int f[10000], fi[10000], inv[10000];
  f[0] = f[1] = fi[0] = fi[1] = inv[0] = inv[1] = 1;
  for (long long int i = 2; i < 10000; i++) {
    f[i] = f[i - 1] * i % 1000000007;
    inv[i] = 1000000007 - inv[1000000007 % i] * (1000000007 / i) % 1000000007;
    fi[i] = fi[i - 1] * inv[i] % 1000000007;
  }
  long long int ans = f[n];
  long long int ak;
  for (long long int i = 1; i <= k; i++) {
    cin >> ak;
    for (long long int prev = 0; prev <= n; prev++) {
      for (long long int cur = 0; cur + prev <= n and cur <= ak; cur++)
        dp[i][cur + prev] =
            (dp[i][cur + prev] + dp[i - 1][prev] * f[n - cur] % 1000000007 *
                                     fi[cur] % 1000000007 * fi[ak - cur] %
                                     1000000007 * fi[n - ak] % 1000000007) %
            1000000007;
    }
  }
  cout << f[n] * dp[k][n] % 1000000007 << endl;
}
