public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int N = sc . nextInt ( ) ;
  char s [ ] = sc . next ( ) . toCharArray ( ) ;
  int [ ] num = new int [ 3 ] ;
  for ( int i = 0 ;
  i < N ;
  i ++ ) {
    switch ( s [ i ] ) {
      case 'R' : num [ 0 ] ++ ;
      break ;
      case 'G' : num [ 1 ] ++ ;
      break ;
      case 'B' : num [ 2 ] ++ ;
      break ;
    }
  }
  int ans = 0 ;
  for ( int i = 0 ;
  i < 3 ;
  i ++ ) {
    ans += num [ i ] % 2 ;
  }
  System . out . println ( ans ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int N = sc . nextInt ( ) ; char s [ ] = sc . next ( ) . toCharArray ( ) ; int [ ] num = new int [ 3 ] ; for ( int i = 0 ; i < N ; i ++ ) { switch ( s [ i ] ) { case ' R ' : num [ 0 ] ++ ; break ; case ' G ' : num [ 1 ] ++ ; break ; case ' B ' : num [ 2 ] ++ ; break ; } } int ans = 0 ; for ( int i = 0 ; i < 3 ; i ++ ) { ans += num [ i ] % 2 ; } System . out . println ( ans ) ; }
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