#include <bits/stdc++.h>
using namespace std;
vector<int> v[10003], v1[10003];
int cnt[10003];
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, m, i, j;
  cin >> m >> n;
  for (i = 0; i < m; i++) {
    int x, y;
    cin >> x;
    memset(cnt, 0, sizeof(cnt));
    for (j = 0; j < x; j++) {
      cin >> y;
      v[i].push_back(y);
      cnt[y]++;
    }
    for (j = 1; j <= n; j++) {
      if (!cnt[j]) v1[i].push_back(j);
    }
    sort(v[i].begin(), v[i].end());
    sort(v1[i].begin(), v1[i].end());
  }
  for (i = 0; i < m; i++)
    for (j = 0; j < m; j++) {
      int fl = 1;
      for (int k = 0; k < v[i].size(); k++) {
        if (!binary_search(v1[j].begin(), v1[j].end(), v[i][k])) fl = 0;
      }
      if (fl) {
        cout << "impossible";
        return 0;
      }
    }
  cout << "possible";
}
