// Source: https://usaco.guide/general/io

#include <bits/stdc++.h>
using namespace std;

const int INF=1e12;

int main() {
    int n,m,ind,erk;cin>>n>>m>>ind>>erk;
    vector<vector<int>> v(n);
    vector<vector<int>> a(m);
    ind--;erk--;
    for(int i = 0;i<n;i++){
        int x;cin>>x;
        for(int j = 0;j<x;j++){
            int b;cin>>b;
            a[--b].push_back(i);
        }
    } 
    for(int i = 0;i<m;i++){
        for(int j = 0;j<a[i].size();j++){
            for(int k = 0;k<j;k++){
                v[a[i][k]].push_back(a[i][j]);
                v[a[i][j]].push_back(a[i][k]);
            }
        }
    }
    queue<int> q;
    vector<int> dis(n,INF);
    for(int i : a[ind]){
        q.push(i);
        dis[i]=1;
    }
    while(!q.empty()){
        int u=q.front();
        q.pop();
        for(int i : v[u]){
            if(dis[i]==INF){
                dis[i]=dis[u]+1;
                q.push(i);
            }
        }
    }
    int ans=0;
    for(int i : a[erk]){
        ans=max(ans,dis[i]);
    }
    cout<<ans<<endl;
}