public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  while ( sc . hasNextInt ( ) ) {
    int N = sc . nextInt ( ) ;
    Map < Long , Integer > cnt = new HashMap < > ( ) ;
    Set < Long > set = new HashSet < > ( ) ;
    for ( int i = 0 ;
    i < N ;
    i ++ ) {
      long x = sc . nextLong ( ) ;
      int nowCnt = cnt . getOrDefault ( x , 0 ) ;
      nowCnt ++ ;
      cnt . put ( x , nowCnt ) ;
      set . add ( x ) ;
    }
    List < Long > sortList = new ArrayList < > ( set ) ;
    sortList . sort ( Long :: compareTo ) ;
    long ans = 0 ;
    List < Long > hen = new ArrayList < > ( ) ;
    for ( int i = sortList . size ( ) - 1 ;
    hen . size ( ) < 2 && i >= 0 ;
    i -- ) {
      long len = sortList . get ( i ) ;
      if ( cnt . get ( len ) >= 2 ) {
        hen . add ( len ) ;
      }
      if ( cnt . get ( len ) >= 4 ) {
        hen . add ( len ) ;
      }
    }
    if ( hen . size ( ) >= 2 ) {
      ans = hen . get ( 0 ) * hen . get ( 1 ) ;
    }
    System . out . println ( ans ) ;
  }
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; while ( sc . hasNextInt ( ) ) { int N = sc . nextInt ( ) ; Map < Long , Integer > cnt = new HashMap < > ( ) ; Set < Long > set = new HashSet < > ( ) ; for ( int i = 0 ; i < N ; i ++ ) { long x = sc . nextLong ( ) ; int nowCnt = cnt . getOrDefault ( x , 0 ) ; nowCnt ++ ; cnt . put ( x , nowCnt ) ; set . add ( x ) ; } List < Long > sortList = new ArrayList < > ( set ) ; sortList . sort ( Long :: compareTo ) ; long ans = 0 ; List < Long > hen = new ArrayList < > ( ) ; for ( int i = sortList . size ( ) - 1 ; hen . size ( ) < 2 && i >= 0 ; i -- ) { long len = sortList . get ( i ) ; if ( cnt . get ( len ) >= 2 ) { hen . add ( len ) ; } if ( cnt . get ( len ) >= 4 ) { hen . add ( len ) ; } } if ( hen . size ( ) >= 2 ) { ans = hen . get ( 0 ) * hen . get ( 1 ) ; } System . out . println ( ans ) ; } }
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