public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int n = sc . nextInt ( ) ;
  Node [ ] gr = new Node [ 4005 ] ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    int u = sc . nextInt ( ) ;
    int v = 2000 + sc . nextInt ( ) ;
    if ( gr [ u ] == null ) {
      gr [ u ] = new Node ( ) ;
    }
    if ( gr [ v ] == null ) {
      gr [ v ] = new Node ( ) ;
    }
    gr [ u ] . adj . add ( v ) ;
    gr [ v ] . adj . add ( u ) ;
  }
  int count = - 1 ;
  for ( int i = 0 ;
  i < gr . length ;
  i ++ ) {
    if ( gr [ i ] != null && ! gr [ i ] . visited ) {
      count ++ ;
      recur ( i , gr ) ;
    }
  }
  System . out . println ( count ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int n = sc . nextInt ( ) ; Node [ ] gr = new Node [ 4005 ] ; for ( int i = 0 ; i < n ; i ++ ) { int u = sc . nextInt ( ) ; int v = 2000 + sc . nextInt ( ) ; if ( gr [ u ] == null ) { gr [ u ] = new Node ( ) ; } if ( gr [ v ] == null ) { gr [ v ] = new Node ( ) ; } gr [ u ] . adj . add ( v ) ; gr [ v ] . adj . add ( u ) ; } int count = - 1 ; for ( int i = 0 ; i < gr . length ; i ++ ) { if ( gr [ i ] != null && ! gr [ i ] . visited ) { count ++ ; recur ( i , gr ) ; } } System . out . println ( count ) ; }
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