// vvvvvvvvvvvv TEMPLATE vvvvvvvvvvvv
#include <bits/stdc++.h>
using namespace std; using ll = long long; using P = pair<ll, ll>;
const ll linf = 1e18; const double eps = 1e-12, pi = acos(-1);
#define FOR(i,a,b) for (ll i=(a),__last_##i=(b);i<__last_##i;i++)
#define RFOR(i,a,b) for (ll i=(b)-1,__last_##i=(a);i>=__last_##i;i--)
#define REP(i,n) FOR(i,0,n)
#define RREP(i,n) RFOR(i,0,n)
#define __GET_MACRO3(_1, _2, _3, NAME, ...) NAME
#define each(i,a) for (auto&& i : a)
#define rep(...) __GET_MACRO3(__VA_ARGS__, FOR, REP)(__VA_ARGS__)
#define rrep(...) __GET_MACRO3(__VA_ARGS__, RFOR, RREP)(__VA_ARGS__)
#define pb push_back
#define eb emplace_back
#define all(a) begin(a),end(a)
#define chmin(x,v) x = min(x, v)
#define chmax(x,v) x = max(x, v)
template<typename T> ll min(ll a, const T&& b) { return a < b ? a : b; }
template<typename T> ll min(const T&& a, ll b) { return a < b ? a : b; }
template<typename T> ll max(ll a, const T&& b) { return a > b ? a : b; }
template<typename T> ll max(const T&& a, ll b) { return a > b ? a : b; }
template<typename Head> void out(Head h) { cout << h << endl; } template<typename Head, typename... Tail>void out(Head h, Tail... t) { cout << h << " "; out(t...); }
template<typename T> istream& operator>>(istream& is, vector<T>& v) { each(x,v) is >> x; return is; }
template<typename T> ostream& operator<<(ostream& os, const vector<T>& v) { rep(i,v.size()) { if (i) os << " "; os << v[i]; } return os; }
ostream& operator<<(ostream& os, const vector<string>& v) { rep(i,v.size()) { if (i) os << endl; os << v[i]; } return os; }
template<typename T> ostream& operator<<(ostream& os, const vector<vector<T>>& v) { rep(i,v.size()) { if (i) os << endl; os << v[i]; } return os; }
template<typename T1, typename T2> ostream& operator<<(ostream& os, const pair<T1, T2>& p) { return os << "(" << p.first << ", " << p.second << ")"; }
struct yes_no : std::numpunct<char> { string_type do_truename() const { return "Yes"; } string_type do_falsename() const { return "No"; } };
void solve(); int main() {
  ios::sync_with_stdio(false); cin.tie(0); locale loc(locale(), new yes_no); cout.imbue(loc); cout << fixed << setprecision(10) << boolalpha;
  solve();
}
// ^^^^^^^^^^^^ TEMPLATE ^^^^^^^^^^^^

ll solve(ll n) {
  vector<vector<bool>> a(n, vector<bool>(31, false));
  rep(i, n) {
    ll k; cin >> k;
    rep(j, k) {
      ll x; cin >> x;
      a[i][x] = true;
    }
  }
  vector<vector<vector<ll>>> vv(n, vector<vector<ll>>(n));
  rep(i, n) rep(j, n) rep(d, 31) {
    if (a[i][d] && a[j][d]) {
      vv[i][j].pb(d);
    }
  }
  rep(D, 1, 31) {
    rep(s, n) {
      vector<ll> d(n, -linf);
      d[s] = D;
      priority_queue<P> Q; Q.push(P(D, s));
      while ( !Q.empty() ) {
        P p = Q.top(); Q.pop();
        ll v = p.second;
        // cout << v << endl;
        if (p.first < d[v]) continue;
        rep(to, n) {
          auto it = upper_bound(all(vv[v][to]), d[v]);
          if (it == vv[v][to].begin()) continue;
          --it;
          ll nd = *it;
          if (nd > d[to]) {
            d[to] = nd;
            Q.push(P(d[to], to));
          }
        }
      }
      bool is_all = true;
      // cout << D << " " << s << " : " << d << endl;
      rep(i, n) if (d[i] < 0) is_all = false;
      if (is_all) {
        return D;
      }
    }
  }
  return -1;
}

void solve() {
  ll n;
  while (cin >> n, n) {
    cout << solve(n) << endl;
  }
}



Measured memory_bytes: 3668