public static void main ( String [ ] args ) {
  Scanner input = new Scanner ( System . in ) ;
  int x , y , a , b ;
  x = input . nextInt ( ) ;
  y = input . nextInt ( ) ;
  a = input . nextInt ( ) ;
  b = input . nextInt ( ) ;
  if ( x <= b ) {
    System . out . println ( 0 ) ;
    return ;
  }
  StringBuilder ans = new StringBuilder ( ) ;
  int count = 0 ;
  for ( int i = a ;
  i <= x ;
  i ++ ) {
    int j = b ;
    while ( i > j && y >= j ) {
      count ++ ;
      ans . append ( i + " " + j + "\n" ) ;
      j ++ ;
    }
  }
  System . out . println ( count ) ;
  System . out . println ( ans ) ;
}

public static void main ( String [ ] args ) { Scanner input = new Scanner ( System . in ) ; int x , y , a , b ; x = input . nextInt ( ) ; y = input . nextInt ( ) ; a = input . nextInt ( ) ; b = input . nextInt ( ) ; if ( x <= b ) { System . out . println ( 0 ) ; return ; } StringBuilder ans = new StringBuilder ( ) ; int count = 0 ; for ( int i = a ; i <= x ; i ++ ) { int j = b ; while ( i > j && y >= j ) { count ++ ; ans . append ( i + " ▁ " + j + " \n " ) ; j ++ ; } } System . out . println ( count ) ; System . out . println ( ans ) ; }
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