public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int n = sc . nextInt ( ) ;
  int d = sc . nextInt ( ) ;
  String [ ] from = new String [ n ] ;
  String [ ] to = new String [ n ] ;
  int [ ] time = new int [ n ] ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    from [ i ] = sc . next ( ) ;
    to [ i ] = sc . next ( ) ;
    time [ i ] = sc . nextInt ( ) ;
  }
  HashSet < String > ans = new HashSet < String > ( ) ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    for ( int j = i + 1 ;
    j < n ;
    j ++ ) {
      if ( from [ i ] . equals ( to [ j ] ) && to [ i ] . equals ( from [ j ] ) && time [ j ] - time [ i ] <= d && time [ j ] - time [ i ] > 0 ) {
        ans . add ( fixStr ( from [ i ] , to [ i ] ) ) ;
      }
    }
  }
  System . out . println ( ans . size ( ) ) ;
  for ( String s : ans ) {
    System . out . println ( s ) ;
  }
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int n = sc . nextInt ( ) ; int d = sc . nextInt ( ) ; String [ ] from = new String [ n ] ; String [ ] to = new String [ n ] ; int [ ] time = new int [ n ] ; for ( int i = 0 ; i < n ; i ++ ) { from [ i ] = sc . next ( ) ; to [ i ] = sc . next ( ) ; time [ i ] = sc . nextInt ( ) ; } HashSet < String > ans = new HashSet < String > ( ) ; for ( int i = 0 ; i < n ; i ++ ) { for ( int j = i + 1 ; j < n ; j ++ ) { if ( from [ i ] . equals ( to [ j ] ) && to [ i ] . equals ( from [ j ] ) && time [ j ] - time [ i ] <= d && time [ j ] - time [ i ] > 0 ) { ans . add ( fixStr ( from [ i ] , to [ i ] ) ) ; } } } System . out . println ( ans . size ( ) ) ; for ( String s : ans ) { System . out . println ( s ) ; } }
(method_declaration (modifiers) type: (void_type) name: (identifier) parameters: (formal_parameters (formal_parameter type: (array_type element: (type_identifier) dimensions: (dimensions)) name: (identifier))) body: (block (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (object_creation_expression type: (type_identifier) arguments: (argument_list (field_access object: (identifier) field: (identifier)))))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (local_variable_declaration type: (array_type element: (type_identifier) dimensions: (dimensions)) declarator: (variable_declarator name: (identifier) value: (array_creation_expression type: (type_identifier) dimensions: (dimensions_expr (identifier))))) (local_variable_declaration type: (array_type element: (type_identifier) dimensions: (dimensions)) declarator: (variable_declarator name: (identifier) value: (array_creation_expression type: (type_identifier) dimensions: (dimensions_expr (identifier))))) (local_variable_declaration type: (array_type element: (integral_type) dimensions: (dimensions)) declarator: (variable_declarator name: (identifier) value: (array_creation_expression type: (integral_type) dimensions: (dimensions_expr (identifier))))) (for_statement init: (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) condition: (binary_expression left: (identifier) right: (identifier)) update: (update_expression (identifier)) body: (block (expression_statement (assignment_expression left: (array_access array: (identifier) index: (identifier)) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (expression_statement (assignment_expression left: (array_access array: (identifier) index: (identifier)) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (expression_statement (assignment_expression left: (array_access array: (identifier) index: (identifier)) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))))) (local_variable_declaration type: (generic_type (type_identifier) (type_arguments (type_identifier))) declarator: (variable_declarator name: (identifier) value: (object_creation_expression type: (generic_type (type_identifier) (type_arguments (type_identifier))) arguments: (argument_list)))) (for_statement init: (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) condition: (binary_expression left: (identifier) right: (identifier)) update: (update_expression (identifier)) body: (block (for_statement init: (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (binary_expression left: (identifier) right: (decimal_integer_literal)))) condition: (binary_expression left: (identifier) right: (identifier)) update: (update_expression (identifier)) body: (block (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (binary_expression left: (method_invocation object: (array_access array: (identifier) index: (identifier)) name: (identifier) arguments: (argument_list (array_access array: (identifier) index: (identifier)))) right: (method_invocation object: (array_access array: (identifier) index: (identifier)) name: (identifier) arguments: (argument_list (array_access array: (identifier) index: (identifier))))) right: (binary_expression left: (binary_expression left: (array_access array: (identifier) index: (identifier)) right: (array_access array: (identifier) index: (identifier))) right: (identifier))) right: (binary_expression left: (binary_expression left: (array_access array: (identifier) index: (identifier)) right: (array_access array: (identifier) index: (identifier))) right: (decimal_integer_literal)))) consequence: (block (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (method_invocation name: (identifier) arguments: (argument_list (array_access array: (identifier) index: (identifier)) (array_access array: (identifier) index: (identifier))))))))))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (method_invocation object: (identifier) name: (identifier) arguments: (argument_list))))) (enhanced_for_statement type: (type_identifier) name: (identifier) value: (identifier) body: (block (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (identifier))))))))