/**
 *  Gather the Maps! (Problem F, Practice Contest for Japan Domestic, 2005-06-19)
 *  by Kenji Inoue, 2007-01-04
 **/

#include <iostream>
#include <set>

using namespace std;

int main() {
  int d[51][31]; // available dates
  int m[51][51]; // maps collected

  int n;
  while (cin >> n, n) {
    memset(d, 0, sizeof(d));
    memset(m, 0, sizeof(m));

    for (int i=0; i<n; i++) {
      int num;
      cin >> num;
      for (int j=0; j<num; j++) {
        int t;
        cin >> t;
        d[i][t] = 1;
      }
      m[i][i] = 1; // he only has his own map
    }

    for (int t=1; t<=30; t++) {
      // find which maps can be collected
      set<int> maps;
      for (int i=0; i<n; i++) {
        if (!d[i][t]) { continue; }

        for (int j=0; j<n; j++) {
          if (m[i][j]) { maps.insert(j); }
        }
      }

      // merge
      for (int i=0; i<n; i++) {
        if (!d[i][t]) { continue; }

        for (set<int>::iterator it = maps.begin(); it != maps.end(); it++) {
          m[i][*it] = 1;
        }
      }

      // check if all gathered
      if (maps.size() == n) {
        cout << t << endl;
        goto NEXT;
      }
    }

    cout << -1 << endl;
  NEXT: ;
  }

  return 0;
}