// 誤解法（愚直O(N^2 M)解）チェックその２
#ifdef DEBUG
  #define _GLIBCXX_DEBUG
  #define UNTIE ios_base::sync_with_stdio( false ); cin.tie( nullptr ); signal( SIGABRT , &AlertAbort )
  #define DEXPR( LL , BOUND , VALUE , DEBUG_VALUE ) CEXPR( LL , BOUND , DEBUG_VALUE )
  #define CERR( MESSAGE ) cerr << MESSAGE << endl;
  #define COUT( ANSWER ) cout << "出力： " << ANSWER << endl
  #define ASSERT( A , MIN , MAX ) CERR( "ASSERTチェック： " << ( MIN ) << ( ( MIN ) <= A ? "<=" : ">" ) << A << ( A <= ( MAX ) ? "<=" : ">" ) << ( MAX ) ); assert( ( MIN ) <= A && A <= ( MAX ) )
#else
  #pragma GCC optimize ( "O3" )
  #pragma GCC optimize( "unroll-loops" )
  #pragma GCC target ( "sse4.2,fma,avx2,popcnt,lzcnt,bmi2" )
  #define UNTIE ios_base::sync_with_stdio( false ); cin.tie( nullptr )
  #define DEXPR( LL , BOUND , VALUE , DEBUG_VALUE ) CEXPR( LL , BOUND , VALUE )
  #define CERR( MESSAGE ) 
  #define COUT( ANSWER ) cout << ANSWER << "\n"
  #define ASSERT( A , MIN , MAX ) assert( ( MIN ) <= A && A <= ( MAX ) )
#endif
#include <bits/stdc++.h>
using namespace std;
#define MAIN main
#define TYPE_OF( VAR ) decay_t<decltype( VAR )>
#define CEXPR( LL , BOUND , VALUE ) constexpr LL BOUND = VALUE
#define CIN( LL , A ) LL A; cin >> A
#define SET_ASSERT( A , MIN , MAX ) cin >> A; ASSERT( A , MIN , MAX )
#define CIN_ASSERT( A , MIN , MAX ) TYPE_OF( MAX ) A; SET_ASSERT( A , MIN , MAX )
#define FOR( VAR , INITIAL , FINAL_PLUS_ONE ) for( TYPE_OF( FINAL_PLUS_ONE ) VAR = INITIAL ; VAR < FINAL_PLUS_ONE ; VAR ++ )
#define FOREQ( VAR , INITIAL , FINAL ) for( TYPE_OF( FINAL ) VAR = INITIAL ; VAR <= FINAL ; VAR ++ )
#define AUTO_ITR( ARRAY ) auto itr_ ## ARRAY = ARRAY .begin() , end_ ## ARRAY = ARRAY .end()
#define FOR_ITR( ARRAY ) for( AUTO_ITR( ARRAY ) , itr = itr_ ## ARRAY ; itr_ ## ARRAY != end_ ## ARRAY ; itr_ ## ARRAY ++ , itr++ )
#define REPEAT( HOW_MANY_TIMES ) FOR( VARIABLE_FOR_REPEAT_ ## HOW_MANY_TIMES , 0 , HOW_MANY_TIMES )
#define QUIT return 0
#define RETURN( ANSWER ) COUT( ( ANSWER ) ); QUIT

#ifdef DEBUG
  inline void AlertAbort( int n ) { CERR( "abort関数が呼ばれました。assertマクロのメッセージが出力されていない場合はオーバーフローの有無を確認をしてください。" ); }
#endif

int MAIN()
{
  UNTIE;
  DEXPR( int , bound_N , 4000 , 100 ); // 0が3個
  CIN_ASSERT( N , 0 , bound_N );
  CIN_ASSERT( M , 1 , N + 1 );
  int A[bound_N*2+1];
  int N2 = N * 2;
  FOREQ( k , 0 , N2 ){
    CIN_ASSERT( Ak , 0 , N );
    A[k] = Ak;
  }
  set<int> S{};
  bool T[bound_N+1] = {};
  FOR( m , 0 , M ){
    CIN( int , sm );
    S.insert( sm );
    T[sm] = true;
  }
  REPEAT( N ){
    bool ST[bound_N+1] = {};
    FOR_ITR( S ){
      FOREQ( j , 0 , N ){
	if( T[j] ){
	  ST[A[*itr+j]] = true;
	}
      }
    }
    bool updated = false;
    FOREQ( i , 0 , N ){
      if( ST[i] ){
	bool& Ti = T[i];
	if( !Ti ){
	  Ti = true;
	  updated = true;
	}
      }
    }
    if( !updated ){
      break;
    }
  }
  int answer = 0;
  FOREQ( i , 0 , N ){
    T[i] ? ++answer : answer;
  }
  RETURN( answer );
}