public static void main ( String args [ ] ) {
  FScanner in = new FScanner ( ) ;
  PrintWriter out = new PrintWriter ( System . out ) ;
  int n = in . nextInt ( ) ;
  int arr [ ] = new int [ n + 1 ] ;
  if ( n % 2 != 0 ) out . println ( "-1" ) ;
  else {
    for ( int i = 1 ;
    i <= n ;
    i ++ ) {
      if ( i % 2 != 0 ) out . print ( i + 1 + " " ) ;
      else out . print ( i - 1 + " " ) ;
    }
  }
  out . close ( ) ;
}

public static void main ( String args [ ] ) { FScanner in = new FScanner ( ) ; PrintWriter out = new PrintWriter ( System . out ) ; int n = in . nextInt ( ) ; int arr [ ] = new int [ n + 1 ] ; if ( n % 2 != 0 ) out . println ( " - 1" ) ; else { for ( int i = 1 ; i <= n ; i ++ ) { if ( i % 2 != 0 ) out . print ( i + 1 + " ▁ " ) ; else out . print ( i - 1 + " ▁ " ) ; } } out . close ( ) ; }
(method_declaration (modifiers) type: (void_type) name: (identifier) parameters: (formal_parameters (formal_parameter type: (type_identifier) name: (identifier) dimensions: (dimensions))) 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: (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) dimensions: (dimensions) value: (array_creation_expression type: (integral_type) dimensions: (dimensions_expr (binary_expression left: (identifier) right: (decimal_integer_literal)))))) (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal))) consequence: (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (string_literal)))) alternative: (block (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 (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (decimal_integer_literal))) consequence: (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (string_literal))))) alternative: (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (binary_expression left: (binary_expression left: (identifier) right: (decimal_integer_literal)) right: (string_literal)))))))))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))))