public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int N = sc . nextInt ( ) ;
  int M = sc . nextInt ( ) ;
  int [ ] x = new int [ M ] ;
  int [ ] y = new int [ M ] ;
  ArrayList [ ] edge = new ArrayList [ N ] ;
  for ( int i = 0 ;
  i < N ;
  i ++ ) {
    edge [ i ] = new ArrayList ( ) ;
  }
  for ( int i = 0 ;
  i < M ;
  i ++ ) {
    x [ i ] = sc . nextInt ( ) - 1 ;
    y [ i ] = sc . nextInt ( ) - 1 ;
    edge [ x [ i ] ] . add ( y [ i ] ) ;
  }
  long [ ] dp = new long [ ( int ) Math . pow ( 2 , N ) ] ;
  dp [ 0 ] = 1 ;
  for ( int i = 1 ;
  i < ( int ) Math . pow ( 2 , N ) ;
  i ++ ) {
    for ( int j = 0 ;
    j < N ;
    j ++ ) {
      if ( ( i & ( 1 << j ) ) != 0 ) {
        boolean flg = true ;
        for ( int k = 0 ;
        k < N ;
        k ++ ) {
          if ( ( i & ( 1 << k ) ) != 0 && edge [ j ] . contains ( k ) ) flg = false ;
        }
        if ( flg ) dp [ i ] += dp [ i - ( 1 << j ) ] ;
      }
    }
  }
  System . out . println ( dp [ ( int ) Math . pow ( 2 , N ) - 1 ] ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int N = sc . nextInt ( ) ; int M = sc . nextInt ( ) ; int [ ] x = new int [ M ] ; int [ ] y = new int [ M ] ; ArrayList [ ] edge = new ArrayList [ N ] ; for ( int i = 0 ; i < N ; i ++ ) { edge [ i ] = new ArrayList ( ) ; } for ( int i = 0 ; i < M ; i ++ ) { x [ i ] = sc . nextInt ( ) - 1 ; y [ i ] = sc . nextInt ( ) - 1 ; edge [ x [ i ] ] . add ( y [ i ] ) ; } long [ ] dp = new long [ ( int ) Math . pow ( 2 , N ) ] ; dp [ 0 ] = 1 ; for ( int i = 1 ; i < ( int ) Math . pow ( 2 , N ) ; i ++ ) { for ( int j = 0 ; j < N ; j ++ ) { if ( ( i & ( 1 << j ) ) != 0 ) { boolean flg = true ; for ( int k = 0 ; k < N ; k ++ ) { if ( ( i & ( 1 << k ) ) != 0 && edge [ j ] . contains ( k ) ) flg = false ; } if ( flg ) dp [ i ] += dp [ i - ( 1 << j ) ] ; } } } System . out . println ( dp [ ( int ) Math . pow ( 2 , N ) - 1 ] ) ; }
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