// Optimal prefix (huffman) code for the uniform distribution with M elements
// should not pass

#include <cstdint>
#include <iostream>
#include <vector>
#include <algorithm>
#include <cassert>
#include <iomanip>
using namespace std;


unsigned int log2(unsigned int n) {
  return 31 - __builtin_clz(n);
}


int main(void) {
  int N;
  cin >> N;
  int M;
  cin >> M;
  vector<uint64_t> lines;
  for (int i = 0; i < M; ++i) {
    uint64_t line = 0;
    int num_stations;
    cin >> num_stations;
    for (int j = 0; j < num_stations; ++j) {
      int station;
      cin >> station;
      uint64_t station_mask = 1ULL << station;
      line |= station_mask;
    }
    lines.push_back(line);
  }
  sort(lines.begin(),lines.end());
  for (int i = 1; i < M; i++) {
    if (lines[i] == lines[i-1]) {
      cout << "not possible" << endl;
      return 0;
    }
  }
  // length for the optimal prefix code for a uniform distribution with M elements
  int d = log2(M);
  // there are (2**(d+1)-M) at level d and (2M-2**(d+1)) at level d+1
  cout << std::setprecision(15) << (d+2-(2<<d)/(double)M) << endl; 
  return 0;
}