public static void main ( String [ ] $ ) {
  Scanner sc = new Scanner ( in ) ;
  int n = sc . nextInt ( ) ;
  long [ ] a = new long [ n ] ;
  long edge1 = 0 , edge2 = 0 ;
  TreeMap < Long , Long > tm = new TreeMap < > ( ) ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    a [ i ] = sc . nextLong ( ) ;
    tm . put ( a [ i ] , tm . getOrDefault ( a [ i ] , 0l ) + 1 ) ;
  }
  while ( tm . size ( ) > 0 && edge1 == 0 ) {
    Map . Entry < Long , Long > temp = tm . pollLastEntry ( ) ;
    if ( temp . getValue ( ) > 1 ) {
      edge1 = temp . getKey ( ) ;
      tm . put ( temp . getKey ( ) , temp . getValue ( ) - 2 ) ;
    }
  }
  while ( tm . size ( ) > 0 && edge2 == 0 ) {
    Map . Entry < Long , Long > temp = tm . pollLastEntry ( ) ;
    if ( temp . getValue ( ) > 1 ) {
      edge2 = temp . getKey ( ) ;
    }
  }
  out . println ( edge1 * edge2 ) ;
}

public static void main ( String [ ] $ ) { Scanner sc = new Scanner ( in ) ; int n = sc . nextInt ( ) ; long [ ] a = new long [ n ] ; long edge1 = 0 , edge2 = 0 ; TreeMap < Long , Long > tm = new TreeMap < > ( ) ; for ( int i = 0 ; i < n ; i ++ ) { a [ i ] = sc . nextLong ( ) ; tm . put ( a [ i ] , tm . getOrDefault ( a [ i ] , 0l ) + 1 ) ; } while ( tm . size ( ) > 0 && edge1 == 0 ) { Map . Entry < Long , Long > temp = tm . pollLastEntry ( ) ; if ( temp . getValue ( ) > 1 ) { edge1 = temp . getKey ( ) ; tm . put ( temp . getKey ( ) , temp . getValue ( ) - 2 ) ; } } while ( tm . size ( ) > 0 && edge2 == 0 ) { Map . Entry < Long , Long > temp = tm . pollLastEntry ( ) ; if ( temp . getValue ( ) > 1 ) { edge2 = temp . getKey ( ) ; } } out . println ( edge1 * edge2 ) ; }
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