public static void main ( String [ ] args ) {
  Scanner scan = new Scanner ( System . in ) ;
  int n = scan . nextInt ( ) , x = scan . nextInt ( ) ;
  HashSet < Integer > set1 = new HashSet < > ( ) , set2 = new HashSet < > ( ) ;
  int [ ] a = new int [ n ] ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    int t = scan . nextInt ( ) ;
    set1 . add ( t ) ;
    a [ i ] = t ;
  }
  if ( set1 . size ( ) != n ) {
    System . out . println ( 0 ) ;
    return ;
  }
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    int tmp = a [ i ] & x ;
    set2 . add ( tmp ) ;
    if ( tmp != a [ i ] && set1 . contains ( tmp ) ) {
      System . out . println ( 1 ) ;
      return ;
    }
  }
  System . out . println ( set2 . size ( ) == n ? - 1 : 2 ) ;
}

public static void main ( String [ ] args ) { Scanner scan = new Scanner ( System . in ) ; int n = scan . nextInt ( ) , x = scan . nextInt ( ) ; HashSet < Integer > set1 = new HashSet < > ( ) , set2 = new HashSet < > ( ) ; int [ ] a = new int [ n ] ; for ( int i = 0 ; i < n ; i ++ ) { int t = scan . nextInt ( ) ; set1 . add ( t ) ; a [ i ] = t ; } if ( set1 . size ( ) != n ) { System . out . println ( 0 ) ; return ; } for ( int i = 0 ; i < n ; i ++ ) { int tmp = a [ i ] & x ; set2 . add ( tmp ) ; if ( tmp != a [ i ] && set1 . contains ( tmp ) ) { System . out . println ( 1 ) ; return ; } } System . out . println ( set2 . size ( ) == n ? - 1 : 2 ) ; }
(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))) 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))) declarator: (variable_declarator name: (identifier) value: (object_creation_expression type: (generic_type (type_identifier) (type_arguments)) arguments: (argument_list)))) (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 (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier)))) (expression_statement (assignment_expression left: (array_access array: (identifier) index: (identifier)) right: (identifier))))) (if_statement condition: (parenthesized_expression (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)) right: (identifier))) consequence: (block (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (decimal_integer_literal)))) (return_statement))) (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 (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (binary_expression left: (array_access array: (identifier) index: (identifier)) right: (identifier)))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier)))) (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (identifier) right: (array_access array: (identifier) index: (identifier))) right: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))))) consequence: (block (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (decimal_integer_literal)))) (return_statement))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (ternary_expression condition: (binary_expression left: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)) right: (identifier)) consequence: (unary_expression operand: (decimal_integer_literal)) alternative: (decimal_integer_literal)))))))