public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int N = Integer . parseInt ( sc . next ( ) ) ;
  HashMap < Long , Pair > map = new HashMap < > ( ) ;
  ArrayList < Pair > l = new ArrayList < > ( ) ;
  for ( int i = 0 ;
  i < N ;
  i ++ ) {
    long c = Long . parseLong ( sc . next ( ) ) ;
    if ( ! map . containsKey ( c ) ) {
      Pair p = new Pair ( c , 1 ) ;
      map . put ( c , p ) ;
      l . add ( p ) ;
    }
    else {
      Pair p = map . get ( c ) ;
      p . cnt ++ ;
    }
  }
  Collections . sort ( l ) ;
  int size = l . size ( ) ;
  Pair p1 = l . get ( size - 1 ) ;
  Pair p2 = l . get ( size - 2 ) ;
  long res = 0 ;
  if ( p1 . cnt >= 4 ) res = p1 . a * p1 . a ;
  else if ( p1 . cnt >= 2 && p2 . cnt >= 2 ) res = p1 . a * p2 . a ;
  System . out . println ( res ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int N = Integer . parseInt ( sc . next ( ) ) ; HashMap < Long , Pair > map = new HashMap < > ( ) ; ArrayList < Pair > l = new ArrayList < > ( ) ; for ( int i = 0 ; i < N ; i ++ ) { long c = Long . parseLong ( sc . next ( ) ) ; if ( ! map . containsKey ( c ) ) { Pair p = new Pair ( c , 1 ) ; map . put ( c , p ) ; l . add ( p ) ; } else { Pair p = map . get ( c ) ; p . cnt ++ ; } } Collections . sort ( l ) ; int size = l . size ( ) ; Pair p1 = l . get ( size - 1 ) ; Pair p2 = l . get ( size - 2 ) ; long res = 0 ; if ( p1 . cnt >= 4 ) res = p1 . a * p1 . a ; else if ( p1 . cnt >= 2 && p2 . cnt >= 2 ) res = p1 . a * p2 . a ; System . out . println ( res ) ; }
(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 (method_invocation object: (identifier) name: (identifier) arguments: (argument_list)))))) (local_variable_declaration type: (generic_type (type_identifier) (type_arguments (type_identifier) (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: (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)))) (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 (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 (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (object_creation_expression type: (type_identifier) arguments: (argument_list (identifier) (decimal_integer_literal))))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier) (identifier)))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))))) alternative: (block (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (identifier))))) (expression_statement (update_expression (field_access object: (identifier) field: (identifier)))))))) (expression_statement (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (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: (type_identifier) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (binary_expression left: (identifier) right: (decimal_integer_literal)))))) (local_variable_declaration type: (type_identifier) declarator: (variable_declarator name: (identifier) value: (method_invocation object: (identifier) name: (identifier) arguments: (argument_list (binary_expression left: (identifier) right: (decimal_integer_literal)))))) (local_variable_declaration type: (integral_type) declarator: (variable_declarator name: (identifier) value: (decimal_integer_literal))) (if_statement condition: (parenthesized_expression (binary_expression left: (field_access object: (identifier) field: (identifier)) right: (decimal_integer_literal))) consequence: (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (field_access object: (identifier) field: (identifier)) right: (field_access object: (identifier) field: (identifier))))) alternative: (if_statement condition: (parenthesized_expression (binary_expression left: (binary_expression left: (field_access object: (identifier) field: (identifier)) right: (decimal_integer_literal)) right: (binary_expression left: (field_access object: (identifier) field: (identifier)) right: (decimal_integer_literal)))) consequence: (expression_statement (assignment_expression left: (identifier) right: (binary_expression left: (field_access object: (identifier) field: (identifier)) right: (field_access object: (identifier) field: (identifier))))))) (expression_statement (method_invocation object: (field_access object: (identifier) field: (identifier)) name: (identifier) arguments: (argument_list (identifier))))))