#include <iostream>
#include <vector>
#include <stack>
#include <bitset>
#include <string>
#include <sstream>
using namespace std;

const int MAXN = 50001;

int main()
{
    int n,k; cin>>n>>k;

    vector<vector<int>> Adj(n+1);
    vector<int> gr(n+1,0);
    vector< bitset<MAXN> > infl(n+1);

    vector<int> x(k);
    for(int i=0;i<k;++i) cin>>x[i];

    while(cin.get()!='\n') ;

    string buff;
    for(int i=0;i<n;++i){
        int to; cin>>to;
        getline(cin,buff);

        istringstream iss(buff);
        int from;
        while(iss>>from){
            Adj[from].push_back(to);
            ++gr[to];
        }
    }

    stack<int> nullgr;
    for(int i=1;i<=n;++i) if(!gr[i]) nullgr.push(i);

    while(!nullgr.empty()){
        int v=nullgr.top(); nullgr.pop();

        for(int i : Adj[v]){
            infl[i]|=infl[v];
            infl[i].set(v);
            --gr[i];
            if(gr[i]==0) nullgr.push(i);
        }
    }

    vector<int> ni(n+1);
    for(int i=1;i<=n;++i) ni[i]=infl[i].count();

    int mx=0;
    int imx=n+1;
    for(int i=0;i<k;++i)
        if(mx<ni[x[i]] || (mx==ni[x[i]] && x[i]<imx) ){
            mx=ni[x[i]];
            imx=x[i];
        }

    cout<<imx<<'\n';
}