#include <stdio.h>
#include <stdlib.h>

int n;
int is_available[64][31];

int solve(int person, int day) /* A Variety of Prim's Method */
{
  int k, t, d, val[64], unseen = (1 << 15);
  int min = n, date[64], n_zero;

  if (!is_available[person][day]) { return 0; }

  for (k = 0; k < n; k++) {
    val[k] = -unseen; date[k] = -1;
  }
  val[n] = -(unseen+1);

  for (k = person; k != n; k = min, min = n) {
    int maxd = 0;
    if (k == person) { date[k] = day; }
    val[k] = -val[k];
    if (val[k] == unseen) { val[k] = 0; }

    for (t = 0; t < n; t++) {

      if (val[t] < 0) {
        for (d = date[k]; d >= 1; d--) {
          int found = 0;
          if (is_available[k][d] && is_available[t][d] && date[t] < d) {
            val[t] = -1; date[t] = d; found = 1;
          }
          if (val[t] >= val[min] && date[t] > maxd) {
            min = t; maxd = date[t];
          }
          if (found) { break; }
        }
      }
    }
  }

  n_zero = 0;
  for (k = 0; k < n; k++) {
    if (val[k] < 0) { return 0; }
    if (val[k] == 0) {
      n_zero++;
      if (n_zero > 1) { return 0; }
    }
  }
  return 1;
}

int main()
{
  int i, j, solved = 0;
  int I;

  for (I = 0; ; I++) {
    scanf("%d", &n); if (n == 0) { break; }
    for (i = 0; i < n; i++) {
      int f;
      for (j = 0; j <= 30; j++) { is_available[i][j] = 0; }
      scanf("%d", &f);
      for (j = 0; j < f; j++) {
        int d;
        scanf("%d", &d);
        is_available[i][d] = 1;
      }
    }


    solved = 0;
    for (i = 1; i <= 30; i++) {
      for (j = 0; j < n; j++) {
        if (solve(j, i)) { printf("%d\n", i); solved = 1; break; }
      }
      if (solved) { break; }
    }
    if (!solved) { printf("-1\n"); }
  }
  return 0;
}