public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int n = sc . nextInt ( ) ;
  int [ ] arr = new int [ n + 5 ] ;
  int [ ] count = new int [ ( int ) 2e5 + 10 ] ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) arr [ i ] = sc . nextInt ( ) ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) for ( int j = i + 1 ;
  j < n ;
  j ++ ) count [ arr [ i ] + arr [ j ] ] ++ ;
  int max = 0 ;
  for ( int i = 0 ;
  i < ( int ) 2e5 + 10 ;
  i ++ ) max = Math . max ( count [ i ] , max ) ;
  System . out . print ( max ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int n = sc . nextInt ( ) ; int [ ] arr = new int [ n + 5 ] ; int [ ] count = new int [ ( int ) 2e5 + 10 ] ; for ( int i = 0 ; i < n ; i ++ ) arr [ i ] = sc . nextInt ( ) ; for ( int i = 0 ; i < n ; i ++ ) for ( int j = i + 1 ; j < n ; j ++ ) count [ arr [ i ] + arr [ j ] ] ++ ; int max = 0 ; for ( int i = 0 ; i < ( int ) 2e5 + 10 ; i ++ ) max = Math . max ( count [ i ] , max ) ; System . out . print ( max ) ; }
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