#include <bits/stdc++.h>
using namespace std;
int n, k;
vector<bool> is_important;
vector<vector<int> > graph;
vector<int> used;
vector<int> res;
bool dfs(int v) {
  used[v] = 1;
  bool f_p = is_important[v];
  for (int u : graph[v]) {
    if (used[u] == 0) {
      f_p = dfs(u) || f_p;
    } else if (used[u] == 1) {
      cout << -1 << endl;
      exit(0);
    }
  }
  used[v] = 2;
  res.push_back(v);
  return f_p;
}
int main() {
  cin >> n >> k;
  is_important.assign(n, false);
  used.assign(n, 0);
  graph.resize(n);
  for (int i = 0; i < k; i++) {
    int x;
    cin >> x;
    is_important[x - 1] = true;
  }
  for (int i = 0; i < n; i++) {
    int m;
    cin >> m;
    for (int j = 0; j < m; j++) {
      int v;
      cin >> v;
      graph[i].push_back(v - 1);
    }
  }
  for (int i = 0; i < n; i++) {
    if (is_important[i] && used[i] == 0) dfs(i);
  }
  cout << res.size() << endl;
  for (int i = 0; i < res.size(); i++) {
    cout << res[i] + 1 << ' ';
  }
  return 0;
}
