#include <bits/stdc++.h>
using namespace std;
const int inf = 1000 * 1000 * 1000;
const int maxN = 1000 + 10;
double c[maxN][maxN];
int n, m;
vector<int> a[maxN];
vector<pair<int, int> > all;
int d[maxN], e[maxN];
double dp[maxN][maxN];
double solve(vector<pair<double, double> > &b, int x, int n) {
  double &res = dp[x][n];
  if (res != -1) return res;
  if (n == 0) return res = (x == 0);
  if (x == 0) {
    res = 1;
    for (int i = 0; i < n; i++) res *= b[i].second;
    return res;
  }
  res = b[n - 1].first * solve(b, x - 1, n - 1) +
        b[n - 1].second * solve(b, x, n - 1);
  return res;
}
int main() {
  ios::sync_with_stdio(false);
  for (int i = 0; i < maxN; i++) c[i][0] = 1;
  for (int i = 1; i < maxN; i++)
    for (int j = 1; j < maxN; j++) c[i][j] = c[i - 1][j - 1] + c[i - 1][j];
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    int x, y;
    cin >> x;
    for (int j = 0; j < x; j++) {
      cin >> y, all.push_back(pair<int, int>(y, i)), a[i].push_back(y);
    }
  }
  sort(all.begin(), all.end());
  int last = all.size() - n;
  int l =
      lower_bound(all.begin(), all.end(), pair<int, int>(all[last].first, -1)) -
      all.begin();
  int h = upper_bound(all.begin(), all.end(),
                      pair<int, int>(all[last].first, inf)) -
          all.begin();
  for (int i = l; i < h; i++) e[all[i].second]++;
  for (int i = h; i < all.size(); i++) d[all[i].second]++;
  double res = 1;
  vector<pair<double, double> > b;
  for (int i = 0; i < m; i++) {
    int t = a[i].size();
    if (!e[i])
      res *= 1 / c[t][d[i]];
    else
      b.push_back(make_pair(1 / c[t][d[i] + 1], 1 / c[t][d[i]]));
  }
  for (int i = 0; i < maxN; i++)
    for (int j = 0; j < maxN; j++) dp[i][j] = -1;
  res *= solve(b, h - last, h - l) / c[h - l][h - last];
  cout << fixed << setprecision(20) << res << endl;
  return 0;
}
