public static void main ( String [ ] args ) throws IOException {
  MyScanner s = new MyScanner ( ) ;
  Print p = new Print ( ) ;
  int n = s . nextInt ( ) ;
  char [ ] att = s . nextLine ( ) . toCharArray ( ) ;
  Stack < Character > st = new Stack < > ( ) ;
  boolean ins = false ;
  for ( int i = 0 ;
  i < att . length ;
  i ++ ) {
    char ch = att [ att . length - 1 - i ] ;
    if ( ch == 'B' ) ins = true ;
    if ( ins ) {
      st . push ( ch ) ;
    }
  }
  n = st . size ( ) ;
  long count = 0 ;
  for ( int i = 0 ;
  i < att . length ;
  i ++ ) {
    if ( att [ i ] == 'B' ) {
      count += ( long ) Math . pow ( 2 , i ) ;
    }
  };
}

public static void main ( String [ ] args ) throws IOException { MyScanner s = new MyScanner ( ) ; Print p = new Print ( ) ; int n = s . nextInt ( ) ; char [ ] att = s . nextLine ( ) . toCharArray ( ) ; Stack < Character > st = new Stack < > ( ) ; boolean ins = false ; for ( int i = 0 ; i < att . length ; i ++ ) { char ch = att [ att . length - 1 - i ] ; if ( ch == ' B ' ) ins = true ; if ( ins ) { st . push ( ch ) ; } } n = st . size ( ) ; long count = 0 ; for ( int i = 0 ; i < att . length ; i ++ ) { if ( att [ i ] == ' B ' ) { count += ( long ) Math . pow ( 2 , i ) ; } } ; }
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