#include <cstdio>
#include <memory.h>
#include <cstdlib>
#include <algorithm>
#include <iostream>
#include <utility>
#include <vector>
#include <set>
#include <map>
#include <cmath>
#include <string>
#include <ctime>

using namespace std;

#define forn( i,n ) for ( int i=0; i<(int)(n); i++ )
#define pb push_back
#define mp make_pair
#define sz(a) (int)((a).size())
typedef long long ll;
typedef long double ld;
typedef pair<int,int> pii;

const ld eps = 1e-10;

int n, kp, path[510];
vector<int> g[510];
ld a[510][510];
int id[510];
ld p[510], np[510];
bool gg[510][510];

int main()
{
  freopen( "in.txt", "r", stdin );
  freopen( "out.txt", "w", stdout );

  scanf( "%d", &n );
  scanf( "%d", &kp );
  forn( i, kp ) scanf( "%d", &path[i] );
  forn( i, n )
  {
    int k, x;
    scanf( "%d", &k );
    forn( j, k )
    {
      scanf( "%d", &x );
      g[i].pb( x );
      gg[i][x] = 1;
    }
  }

  forn( i, n )
  {
    forn( j, g[i].size() )
      a[ g[i][j] ][i] = 1.0 / g[i].size();
    a[i][i] -= 1.0;
  }

  forn( i, n ) a[n-1][i] = 1.0;
  a[n-1][n] = 1.0;
/*
  forn( i, n )
  {
    forn( j, n+1 ) printf( "%.3f ", (double)a[i][j] );
    printf( "\n" );
  }
*/
  forn( i, n ) id[i] = i;

  int N = n+1;
  forn( i, n )
  {
    int j;
    for ( j=i; j<n; j++ )
      if ( fabs( a[ id[j] ][i] ) > eps ) break;

    swap( id[i], id[j] );

    for ( j=i+1; j<n; j++ )
    {
      ld coeff = -a[ id[j] ][i] / a[ id[i] ][i];
      for ( int q=i; q<N; q++ ) a[ id[j] ][q] += coeff * a[ id[i] ][q];
    }
  }

  for ( int i=n-1; i>=0; i-- )
  {
    p[ id[i] ] = a[ id[i] ][n];
    for ( int j=i+1; j<n; j++ ) p[ id[i] ] -= p[ id[j] ] * a[ id[i] ][j];
    p[ id[i] ] /= a[ id[i] ][i];
  }

//  forn( i, n ) printf( "%.3f ", (double)p[i] ); printf( "\n" );
  forn( i, kp )
  {
    p[ path[i] ] = 0;
    if ( i < kp-1 )
    {
      forn( j, n ) np[j] = 0;
      forn( j, n )
        forn( q, g[j].size() )
          if ( j != path[i+1] || g[j][q] != path[i] )
            np[ g[j][q] ] += p[j] / g[j].size();
      forn( j, n ) p[j] = np[j];
    }
  }

  ld ans = 0;
  forn( j, n ) ans += p[j];

  printf( "%.10f\n", double(ans) );

  return 0;
}