public static void main ( String [ ] args ) {
  FastScanner scanner = new FastScanner ( ) ;
  int n = scanner . nextInt ( ) ;
  TreeSet < Integer > set = new TreeSet < > ( ) ;
  int max = 0 ;
  for ( int i = 0 ;
  i < n * 2 ;
  i ++ ) {
    Integer x = scanner . nextInt ( ) ;
    if ( ! set . contains ( x ) ) {
      set . add ( x ) ;
    }
    else {
      set . remove ( x ) ;
    }
    max = Math . max ( max , set . size ( ) ) ;
  }
  System . out . println ( max ) ;
}

public static void main ( String [ ] args ) { FastScanner scanner = new FastScanner ( ) ; int n = scanner . nextInt ( ) ; TreeSet < Integer > set = new TreeSet < > ( ) ; int max = 0 ; for ( int i = 0 ; i < n * 2 ; i ++ ) { Integer x = scanner . nextInt ( ) ; if ( ! set . contains ( x ) ) { set . add ( x ) ; } else { set . remove ( x ) ; } max = Math . max ( max , set . size ( ) ) ; } System . out . println ( max ) ; }
(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)))) (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: (generic_type (type_identifier) (type_arguments (type_identifier))) declarator: (variable_declarator name: (identifier) value: (object_creation_expression type: (generic_type (type_identifier) (type_arguments)) arguments: (argument_list)))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) (for_statement init: (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) condition: (binary_expression left: (identifier) right: (binary_expression left: (identifier) right: (decimal_integer_literal))) update: (update_expression (identifier)) body: (block (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (if_statement condition: (parenthesized_expression (unary_expression operand: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))))) consequence: (block (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))))) alternative: (block (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier)))))) (expression_statement (assignment_expression left: (identifier) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier) (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (identifier))))))