#include <bits/stdc++.h>

using namespace std;

const int MAX_N = 5005;
vector<int> G[MAX_N];
bitset<MAX_N> bi[MAX_N];
bool vis[MAX_N], isX[MAX_N];

void init() {
    for (int i = 0; i < MAX_N; ++i)  {
        G[i].clear();
        bi[i].reset();
        bi[i].set(i);
        vis[i] = false;
    }
}

void dfs(int cur) {
    vis[cur] = true;
    int size = G[cur].size();
    for (int i = 0; i < size; i++) {
        int now = G[cur][i];
        if (!vis[now]) dfs(now);
        bi[cur] |= bi[now];
    }
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n, k, num, x;
    while (~scanf("%d %d", &n, &k)) {
        init();
        for (int i = 0; i < k; ++i) {
            scanf("%d", &num);
            isX[num] = true;
        }
        string s;
        for (int i = 1; i <= n; ++i) {
            scanf("%d", &num);
            getline(cin, s);
            stringstream ss(s);
            while (ss >> x) G[num].push_back(x);
        }
        int ans = 0, id;
        for (int i = 1; i <= n; ++i) {
            if (!vis[i]) dfs(i);
            int tmp = bi[i].count();
            if (isX[i] && (tmp > ans || (tmp == ans && i < id))) {
                ans = tmp;
                id = i;
            }
        }
        printf("%d\n", id);
    }
    return 0;
}