public static void main ( String [ ] args ) {
  SC sc = new SC ( System . in ) ;
  String s = sc . next ( ) ;
  int [ ] alpha = new int [ 26 ] ;
  for ( int i = 0 ;
  i < 26 ;
  i ++ ) {
    alpha [ i ] = 0 ;
  }
  for ( int i = 0 ;
  i < s . length ( ) ;
  i ++ ) {
    alpha [ ( s . charAt ( i ) ) - 97 ] ++ ;
  }
  int kisu = 0 ;
  int use = 0 ;
  for ( int i = 0 ;
  i < 26 ;
  i ++ ) {
    if ( alpha [ i ] % 2 == 1 ) {
      use += alpha [ i ] - 1 ;
      kisu ++ ;
    }
    else {
      use += alpha [ i ] ;
    }
  }
  if ( kisu == 0 ) {
    System . out . println ( ( use ) ) ;
  }
  else {
    System . out . println ( ( 1 + 2 * ( use / ( kisu * 2 ) ) ) ) ;
  }
}

public static void main ( String [ ] args ) { SC sc = new SC ( System . in ) ; String s = sc . next ( ) ; int [ ] alpha = new int [ 26 ] ; for ( int i = 0 ; i < 26 ; i ++ ) { alpha [ i ] = 0 ; } for ( int i = 0 ; i < s . length ( ) ; i ++ ) { alpha [ ( s . charAt ( i ) ) - 97 ] ++ ; } int kisu = 0 ; int use = 0 ; for ( int i = 0 ; i < 26 ; i ++ ) { if ( alpha [ i ] % 2 == 1 ) { use += alpha [ i ] - 1 ; kisu ++ ; } else { use += alpha [ i ] ; } } if ( kisu == 0 ) { System . out . println ( ( use ) ) ; } else { System . out . println ( ( 1 + 2 * ( use / ( kisu * 2 ) ) ) ) ; } }
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