static void solve ( ) {
  int n = in . nextInt ( ) ;
  int [ ] a = new int [ n ] ;
  int [ ] x = new int [ n ] ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    a [ i ] = in . nextInt ( ) ;
    if ( ( n + 1 ) % 2 != a [ i ] % 2 ) {
      out . println ( 0 ) ;
      return ;
    }
    x [ a [ i ] ] ++ ;
    if ( x [ a [ i ] ] > 2 ) {
      out . println ( 0 ) ;
      return ;
    }
  }
  if ( x [ 0 ] > 1 ) {
    out . println ( 0 ) ;
    return ;
  }
  out . println ( modPow ( 2 , n / 2 , MOD ) ) ;
}

static void solve ( ) { int n = in . nextInt ( ) ; int [ ] a = new int [ n ] ; int [ ] x = new int [ n ] ; for ( int i = 0 ; i < n ; i ++ ) { a [ i ] = in . nextInt ( ) ; if ( ( n + 1 ) % 2 != a [ i ] % 2 ) { out . println ( 0 ) ; return ; } x [ a [ i ] ] ++ ; if ( x [ a [ i ] ] > 2 ) { out . println ( 0 ) ; return ; } } if ( x [ 0 ] > 1 ) { out . println ( 0 ) ; return ; } out . println ( modPow ( 2 , n / 2 , MOD ) ) ; }
(method_declaration (modifiers) type: (void_type) name: (identifier) parameters: (formal_parameters) body: (block (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: (integral_type) dimensions: (dimensions)) declarator: (variable_declarator name: (identifier) value: (array_creation_expression type: (integral_type) 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)))) (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (parenthesized_expression (binary_expression left: (identifier) right: (decimal_integer_literal))) right: (decimal_integer_literal)) right: (binary_expression left: (array_access array: (identifier) index: (identifier)) right: (decimal_integer_literal)))) consequence: (block (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (decimal_integer_literal)))) (return_statement))) (expression_statement (update_expression (array_access array: (identifier) index: (array_access array: (identifier) index: (identifier))))) (if_statement condition: (parenthesized_expression (binary_expression left: (array_access array: (identifier) index: (array_access array: (identifier) index: (identifier))) right: (decimal_integer_literal))) consequence: (block (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (decimal_integer_literal)))) (return_statement))))) (if_statement condition: (parenthesized_expression (binary_expression left: (array_access array: (identifier) index: (decimal_integer_literal)) right: (decimal_integer_literal))) consequence: (block (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (decimal_integer_literal)))) (return_statement))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (method_invocation name: (identifier) arguments: (argument_list (decimal_integer_literal) (binary_expression left: (identifier) right: (decimal_integer_literal)) (identifier))))))))