#include "stdafx.h"
#include <iostream>
#include <vector>
#include <set>
#include <map>
#include <string>
#include <algorithm>
#include <cmath>

using namespace std;
bool fl = false;
void dfs(int &v, vector<vector<int>> &a, vector<int> &used, vector<int> &ans)
{
	used[v] = 1;
	for (int i = 0; i < a[v].size(); ++i)
		if (used[a[v][i]] == 0)
			dfs(a[v][i], a, used, ans);
		else
			if(used[a[v][i]] == 1)
				fl = true;
	used[v] = 2;
	ans.push_back(v);
}

void main()
{
#ifdef _DEBUG
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);
#endif
	int n, k;
	cin >> n >> k;
	vector<vector<int>> a(n);
	vector<int> b(k);
	vector<int> used(n);
	vector<int> ans;
	for (int i = 0; i < k; ++i)
	{
		cin >> b[i];
		b[i]--;
	}
	for (int i = 0; i < n; ++i)
	{
		int m;
		cin >> m;
		for (int j = 0; j < m; ++j)
		{
			int ch;
			cin >> ch;
			ch--;
			a[i].push_back(ch);
			//a[ch].push_back(i);
		}
	}
	for (int i = 0; i < k; ++i)
	{
		if(used[b[i]] == 0)
			dfs(b[i], a, used, ans);
	}
	if (fl)
	{
		cout << -1;
		return;
	}
	cout << ans.size() << endl;
	for (int i = 0; i < ans.size(); ++i)
		cout << ++ans[i] << " ";
}