public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int N = Integer . parseInt ( sc . next ( ) ) ;
  int M = Integer . parseInt ( sc . next ( ) ) ;
  Node [ ] nodes = new Node [ N ] ;
  for ( int i = 0 ;
  i < N ;
  i ++ ) nodes [ i ] = new Node ( i ) ;
  for ( int i = 0 ;
  i < M ;
  i ++ ) {
    Node x = nodes [ Integer . parseInt ( sc . next ( ) ) - 1 ] ;
    Node y = nodes [ Integer . parseInt ( sc . next ( ) ) - 1 ] ;
    x . neighbor . put ( y , 1 ) ;
  }
  sc . close ( ) ;
  int S = 1 << N ;
  long [ ] dp = new long [ S ] ;
  dp [ 0 ] = 1 ;
  Queue < Integer > que = new ArrayDeque < > ( ) ;
  que . add ( 0 ) ;
  while ( ! que . isEmpty ( ) ) {
    int s = que . remove ( ) ;
    for ( int i = 0 ;
    i < N ;
    i ++ ) {
      if ( ( 1 << i & s ) > 0 ) continue ;
      boolean check = true ;
      for ( int j = 0 ;
      j < N ;
      j ++ ) {
        if ( ( 1 << j & s ) > 0 && nodes [ i ] . neighbor . containsKey ( nodes [ j ] ) ) {
          check = false ;
          break ;
        }
      }
      if ( check ) {
        if ( dp [ s + ( 1 << i ) ] == 0 ) {
          que . add ( s + ( 1 << i ) ) ;
        }
        dp [ s + ( 1 << i ) ] += dp [ s ] ;
      }
    }
  }
  System . out . println ( dp [ S - 1 ] ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int N = Integer . parseInt ( sc . next ( ) ) ; int M = Integer . parseInt ( sc . next ( ) ) ; Node [ ] nodes = new Node [ N ] ; for ( int i = 0 ; i < N ; i ++ ) nodes [ i ] = new Node ( i ) ; for ( int i = 0 ; i < M ; i ++ ) { Node x = nodes [ Integer . parseInt ( sc . next ( ) ) - 1 ] ; Node y = nodes [ Integer . parseInt ( sc . next ( ) ) - 1 ] ; x . neighbor . put ( y , 1 ) ; } sc . close ( ) ; int S = 1 << N ; long [ ] dp = new long [ S ] ; dp [ 0 ] = 1 ; Queue < Integer > que = new ArrayDeque < > ( ) ; que . add ( 0 ) ; while ( ! que . isEmpty ( ) ) { int s = que . remove ( ) ; for ( int i = 0 ; i < N ; i ++ ) { if ( ( 1 << i & s ) > 0 ) continue ; boolean check = true ; for ( int j = 0 ; j < N ; j ++ ) { if ( ( 1 << j & s ) > 0 && nodes [ i ] . neighbor . containsKey ( nodes [ j ] ) ) { check = false ; break ; } } if ( check ) { if ( dp [ s + ( 1 << i ) ] == 0 ) { que . add ( s + ( 1 << i ) ) ; } dp [ s + ( 1 << i ) ] += dp [ s ] ; } } } System . out . println ( dp [ S - 1 ] ) ; }
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