#include <bits/stdc++.h>
using namespace std;
const int todx[] = {-2, -2, -1, -1, 1, 1, 2, 2};
const int tody[] = {-1, 1, -2, 2, -2, 2, -1, 1};
bool sortbysec(const pair<long long, long long> &a,
               const pair<long long, long long> &b) {
  return (a.second < b.second);
}
void func(void) {
  freopen("input.txt", "r", stdin);
  freopen("output.txt", "w", stdout);
}
long long gcd(long long a, long long b) {
  if (b == 0)
    return a;
  else
    return gcd(b, a % b);
}
void printStack(stack<string> s) {
  if (s.empty()) return;
  string x = s.top();
  s.pop();
  printStack(s);
  cout << x;
  s.push(x);
}
long long binaryexp(long long n, long long p) {
  if (p == 0) return 1;
  if (p % 2 == 0)
    return binaryexp((n % 1000000009) * (n % 1000000009), p / 2);
  else
    return ((n % 1000000009) *
            binaryexp(((n % 1000000009) * (n % 1000000009)) % 1000000009,
                      (p - 1) / 2) %
            1000000009);
}
vector<long long> spf(10000001, 0);
void siv() {
  spf[1] = 1;
  for (long long i = 2; i < 10000001; i++) spf[i] = i;
  for (long long i = 4; i < 10000001; i += 2) {
    spf[i] = 2;
  }
  for (long long i = 3; i * i < 10000001; i++) {
    if (spf[i] == i) {
      for (long long j = i * i; j < 10000001; j += i) {
        if (spf[j] == j) {
          spf[j] = i;
        }
      }
    }
  }
}
vector<int> m(100007, 0);
vector<int> g[100007];
vector<int> vis(100007, -1);
int n, k, me;
int flag1 = 0;
vector<int> st;
void topological(int i) {
  if (flag1) return;
  vis[i] = 1;
  for (auto x : g[i]) {
    if (vis[x] == 1) {
      flag1 = 1;
      return;
    }
    if (vis[x] == -1) {
      topological(x);
    }
  }
  vis[i] = 2;
  st.push_back(i);
}
int main() {
  cin >> n >> k;
  for (int i = 1; i <= k; i++) {
    cin >> m[i];
  }
  for (int i = 1; i <= n; i++) {
    cin >> me;
    for (int j = 0; j < me; j++) {
      int x;
      cin >> x;
      g[i].push_back(x);
    }
  }
  for (int i = 1; i <= k; i++) {
    if (vis[m[i]] == -1) topological(m[i]);
  }
  if (flag1) {
    cout << -1 << endl;
    return 0;
  }
  cout << st.size() << endl;
  for (auto x : st) {
    cout << x << " ";
  }
}
