#include <bits/stdc++.h>
using namespace std;
template <class t>
t mag(t a) {
  return a > 0 ? a : -a;
}
template <class T, class U>
T cdiv(T num, U den) {
  return (num / den) + ((num % den) > 0);
}
std::ifstream term("/dev/tty");
std::string tempstring;
using ll = int_fast64_t;
using ii = pair<int, int>;
using vi = vector<int>;
using vl = vector<ll>;
using vii = vector<ii>;
const int sij = 60;
const ll mod = 1000000007ll;
vi took[sij];
int m, n;
int esc(int tcase) {
  cin >> m >> n;
  for (auto i = 0; i != m; i++) {
    int tp;
    cin >> tp;
    for (auto j = 0; j != tp; j++) {
      int k;
      cin >> k;
      took[i].push_back(k);
    }
    sort(took[i].begin(), took[i].end());
  }
  for (auto i = 0; i != m - 1; i++) {
    set<int> vv;
    ;
    for (auto &e : took[i]) {
      for (auto j = i + 1; j != m; j++) {
        ;
        ;
        if (binary_search(took[j].begin(), took[j].end(), e)) {
          vv.insert(j);
        }
      }
    };
    if (vv.size() + i + 1 != m) {
      cout << "impossible\n";
      exit(0);
    }
  }
  cout << "possible\n";
  return 0;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int tc = 1;
  for (int i = 1; i <= tc; i++) esc(i);
}
