#include<iostream>
#include<vector>
#include<algorithm>
#include<cmath>
#include<map>
#include<queue>
#include<string>
#include<set>
using namespace std;
typedef long long ll;
int main()
{
    ll n;
    cin >> n;
    vector<vector<ll>>g(n, vector<ll>(n,1e18));
    ll m;
    cin >> m;
    vector<vector<ll>>ed(m);
    map<ll, vector<ll>>a;
    for (int i = 0; i < m; i++) {
        ll k;
        cin >> k;
        for (int j = 0; j < k; j++) {
            ll x;
            cin >> x;
            ed[i].push_back(x);
            a[x].push_back(i);
        }
    }
    ll s, f;
    cin >> s >> f;
    vector<ll>d(n+1,1e18);
    queue<ll>q;
    q.push(s);
    d[s] = -1;
    while (!q.empty()) {
        ll v = q.front();
        q.pop();
        for (auto i : a[v]) {
            for (auto j : ed[i])
                if (d[j] > d[v] + 1) {
                    d[j] = min(d[j], d[v] + 1);
                    q.push(j);
                }
        }
    }
    if (d[f] == 1e18)
        cout << -1;
    else if (f == s)
        cout << 0;
    else
        cout << d[f];
    return 0;
}