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#include <stdint.h>
#include <vector>
#include <iostream>
#include <utility>

using namespace std;


int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  
  unsigned int n, m;
  cin >> n >> m;
  
  vector< vector<int> > reps(n);
  for(unsigned int i = 0; i < n; ++i) {
    int l;
    cin >> l;
    reps[i].resize(l);
    for(int j = 0; j < l; ++j) {
      cin >> reps[i][j]; --reps[i][j];
    }
  }
  
  vector<int> needle(m);
  for(unsigned int i = 0; i < m; ++i) {
    cin >> needle[i]; --needle[i];
  }
  
  vector<int> pmt(m + 1);
  {
    pmt[0] = -1;
    pmt[1] = 0;
    for(unsigned int i = 2, s = 0; i <= m; ++i) {
      while(needle[i - 1] != needle[s] and s != 0) s = pmt[s];
      s += (needle[i - 1] == needle[s]);
      pmt[i] = s;
    }
  }
  
  unsigned int const LIMIT = 50000000;
  vector< pair<int16_t, int16_t> > hay;
  hay.push_back(make_pair<int16_t, int16_t>(0, 1));
  
  for(unsigned int i = 0, s = 0; i < LIMIT ; ++i)  {
    int v = hay[i].first;
    int d = hay[i].second;
    for(unsigned int k = 0; k < reps[v].size() and hay.size() <= LIMIT; ++k) hay.push_back(make_pair<int16_t, int16_t>(reps[v][k], d + 1));
    
    if(i != 0 and d != hay[i - 1].second) s = 0;
    
    while(v != needle[s] and s) s = pmt[s];
    s += (v == needle[s]);
    
    if(s == m) {
      cout << d << '\n';
      return 0;
    }
  }
  
  cout << "-1\n";
  
  return 0;
}