#include <bits/stdc++.h>

using namespace std;

#define ll long long
#define endl "\n"
#define pll pair<ll,ll>
#define vll vector<ll>
#define mll map<ll,ll>
#define fs first
#define sc second

const ll MOD = 1e9+7;


void solve()
{
	ll n, m, ind, erk;
	cin >> n >> m >> ind >> erk;
    ind--; erk--;
	map<ll,set<ll>> l;
    map<ll,set<ll>> s;
    map<ll,set<ll>> e;
    map<ll,ll> erk_stat;
    for(ll i = 0; i < n; i++)
    {
        ll k;
        cin >> k;
        for(ll j = 0; j < k; j++)
        {
            ll inp;
            cin >> inp;
            inp--;
            if(inp == erk)
                erk_stat[i] = 1;
            l[i].insert(inp);
            for(ll p : s[inp])
            {
                e[i].insert(p);
                e[p].insert(i);
            }
            s[inp].insert(i);
        }
    }
    map<ll, vector<ll>> ans;
    queue<ll> q;
    for(ll i : s[ind])
    {
        q.push(i);
        ans[i] = {i};
    }
    while(!q.empty())
    {
        ll p = q.front();
        q.pop();
        if(erk_stat[p] != 1)
            for(ll p2 : e[p])
            {
                if(ans[p2].size() == 0 || ans[p2].size() > ans[p].size()+1)
                {
                    ans[p2] = ans[p];
                    ans[p2].push_back(p2);
                    q.push(p2);
                }
            }
    }
    ll min_v = LLONG_MAX;
    ll min_index = 0;
    for(ll i : s[erk])
    {
        if(ans[i].size() < min_v && ans[i].size() != 0)
        {
            min_v = ans[i].size();
            min_index = i;
        }
    }

    if(min_v == LLONG_MAX)
    {
        cout << -1 << endl;
        return;
    }

    cout << min_v << endl;
    for(ll i : ans[min_index]) cout << i+1 << " ";
    cout << endl;
}

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL); cout.tie(NULL);
    ll t = 1;
    //cin >> t;
    while(t--)
        solve();
    return 0;
}