public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int n = sc . nextInt ( ) ;
  int k = sc . nextInt ( ) ;
  char [ ] s = sc . next ( ) . toCharArray ( ) ;
  char [ ] ans = new char [ n ] ;
  LinkedList < Character > list = new LinkedList < > ( ) ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    list . add ( s [ i ] ) ;
  }
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    PriorityQueue < Character > pq = new PriorityQueue < > ( ) ;
    for ( int j = 0 ;
    j < list . size ( ) ;
    j ++ ) {
      pq . add ( list . get ( j ) ) ;
    }
    loop : while ( true ) {
      char first = pq . poll ( ) ;
      int tmp = k ;
      LinkedList < Character > tmpList = ( LinkedList < Character > ) list . clone ( ) ;
      tmpList . remove ( ( Character ) first ) ;
      if ( first != s [ i ] ) {
        tmp -- ;
        if ( tmp < 0 ) continue ;
      }
      for ( int j = i + 1 ;
      j < n ;
      j ++ ) {
        if ( tmpList . contains ( ( Character ) s [ j ] ) ) {
          tmpList . remove ( ( Character ) s [ j ] ) ;
        }
        else {
          tmp -- ;
          if ( tmp < 0 ) continue loop ;
        }
      }
      if ( first != s [ i ] ) k -- ;
      ans [ i ] = first ;
      list . remove ( ( Character ) first ) ;
      break ;
    }
  }
  System . out . println ( String . valueOf ( ans ) ) ;
  sc . close ( ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int n = sc . nextInt ( ) ; int k = sc . nextInt ( ) ; char [ ] s = sc . next ( ) . toCharArray ( ) ; char [ ] ans = new char [ n ] ; LinkedList < Character > list = new LinkedList < > ( ) ; for ( int i = 0 ; i < n ; i ++ ) { list . add ( s [ i ] ) ; } for ( int i = 0 ; i < n ; i ++ ) { PriorityQueue < Character > pq = new PriorityQueue < > ( ) ; for ( int j = 0 ; j < list . size ( ) ; j ++ ) { pq . add ( list . get ( j ) ) ; } loop : while ( true ) { char first = pq . poll ( ) ; int tmp = k ; LinkedList < Character > tmpList = ( LinkedList < Character > ) list . clone ( ) ; tmpList . remove ( ( Character ) first ) ; if ( first != s [ i ] ) { tmp -- ; if ( tmp < 0 ) continue ; } for ( int j = i + 1 ; j < n ; j ++ ) { if ( tmpList . contains ( ( Character ) s [ j ] ) ) { tmpList . remove ( ( Character ) s [ j ] ) ; } else { tmp -- ; if ( tmp < 0 ) continue loop ; } } if ( first != s [ i ] ) k -- ; ans [ i ] = first ; list . remove ( ( Character ) first ) ; break ; } } System . out . println ( String . valueOf ( ans ) ) ; sc . close ( ) ; }
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