#include <iostream>
#include <vector>

using namespace std;

int K,N;
std::vector<std::vector<int> > pole;

bool is_enough(int i)
{
  int celk = 0;
  int was[K+1];
  for(int ii=0;ii<K+1;ii++) was[ii] = 0;
  int beg=0,end=0;
  int zmr=0;
  while(beg!=N)
    {
      if(zmr<=i)
	{
	  if(celk == K) return true;
	  for(int &j:pole[end])
	    {
	      if(was[j] == 0)
		celk++;
	      was[j]++;
	    }
	  zmr+=pole[end].size();
	  end++;
	  end%=N;
	}
      else
	{
	  for(int &j:pole[beg])
	    {
	      if(was[j] == 1)
		celk--;
	      was[j]--;
	    }
	  zmr-=pole[beg].size();
	  beg++;
	}
    }
  return false;
}

int main()
{
  std::ios::sync_with_stdio(false);
  while(std::cin >> N >> K)
    {
      pole.resize(N);
      int velik_sum = 0;
      for(int i=0;i<N;i++)
	{
	  int l;
	  std::cin >> l;
	  velik_sum += l;
	  for(int i=0;i<l;i++)
	    {
	      int tmp;
	      std::cin >> tmp;
	      pole[i].push_back(tmp);
	    }
	}

      int down = K-1;
      int up = velik_sum+2;
      while(down+1 < up)
	{
	  int i = (down+up)/2;
	  if(is_enough(i)) up = i;
	  else down = i;
	}
      if(up < velik_sum+1) std::cout << up << std::endl;
      else std::cout << -1 << std::endl;
    }

}