#include <bits/stdc++.h>
using namespace std;
int n, k, a[21];
int dp[21][1005];
int C[1005][1005];
int main() {
  cin >> n >> k;
  for (int i = 1; i <= k; i++) cin >> a[i];
  C[0][0] = 1;
  for (int i = 1; i <= n; i++) {
    C[i][0] = 1;
    for (int j = 1; j <= i; j++)
      C[i][j] = (C[i - 1][j - 1] + C[i - 1][j]) % 1000000007;
  }
  dp[0][0] = 1;
  for (int i = 1; i <= k; i++) {
    for (int j = 0; j <= n; j++) {
      if (!dp[i - 1][j]) continue;
      for (int l = 0; l <= j; l++) {
        for (int r = 0; r <= a[i] - l; r++) {
          (dp[i][j + r] += 1ll * C[j][l] * C[n - j][a[i] - l] % 1000000007 *
                           C[a[i] - l][r] % 1000000007 * dp[i - 1][j] %
                           1000000007) %= 1000000007;
        }
      }
    }
  }
  printf("%d\n", dp[k][n]);
  return 0;
}
