public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int n = sc . nextInt ( ) ;
  int [ ] p = new int [ n ] ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) p [ i ] = sc . nextInt ( ) ;
  int max = 0 ;
  int q = 0 ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    int r = p [ i ] ;
    while ( r != - 1 ) {
      q ++ ;
      max = Math . max ( max , q ) ;
      r = p [ r - 1 ] ;
    }
    q = 0 ;
  }
  System . out . println ( max + 1 ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int n = sc . nextInt ( ) ; int [ ] p = new int [ n ] ; for ( int i = 0 ; i < n ; i ++ ) p [ i ] = sc . nextInt ( ) ; int max = 0 ; int q = 0 ; for ( int i = 0 ; i < n ; i ++ ) { int r = p [ i ] ; while ( r != - 1 ) { q ++ ; max = Math . max ( max , q ) ; r = p [ r - 1 ] ; } q = 0 ; } System . out . println ( max + 1 ) ; }
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