#include <bits/stdc++.h>
using namespace std;
struct custom_hash {
  static uint64_t splitmix64(uint64_t x) {
    x += 0x9e3779b97f4a7c15;
    x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
    x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
    return x ^ (x >> 31);
  }
  size_t operator()(uint64_t x) const {
    static const uint64_t FIXED_RANDOM =
        chrono::steady_clock::now().time_since_epoch().count();
    return splitmix64(x + FIXED_RANDOM);
  }
};
void shoot() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
}
int main() {
  shoot();
  long long i, j, m, n, k, x, y;
  cin >> m >> n;
  vector<long long> v[m];
  for (i = 0; i < m; i++) {
    cin >> k;
    for (j = 0; j < k; j++) {
      cin >> x;
      v[i].push_back(x);
    }
    sort(v[i].begin(), v[i].end());
  }
  for (i = 0; i < m; i++) {
    for (j = i + 1; j < m; j++) {
      bool ok = false;
      x = 0, y = 0;
      while (x < v[i].size() && y < v[j].size()) {
        if (v[i][x] == v[j][y]) {
          ok = true;
          break;
        } else if (v[i][x] < v[j][y])
          x++;
        else
          y++;
      }
      if (!ok) {
        cout << "impossible";
        return 0;
      }
    }
  }
  cout << "possible";
  return 0;
}
