public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int N = sc . nextInt ( ) ;
  int K = sc . nextInt ( ) ;
  sc . nextLine ( ) ;
  S = sc . nextLine ( ) ;
  char [ ] c = S . toCharArray ( ) ;
  Arrays . sort ( c ) ;
  String ans = "" ;
  for ( int i = 0 ;
  i < N ;
  i ++ ) {
    for ( int j = 0 ;
    j < N ;
    j ++ ) {
      if ( c [ j ] == '\0' ) continue ;
      if ( count ( ans , c , c [ j ] ) > K ) continue ;
      ans += c [ j ] ;
      c [ j ] = '\0' ;
      break ;
    }
  }
  System . out . println ( ans ) ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int N = sc . nextInt ( ) ; int K = sc . nextInt ( ) ; sc . nextLine ( ) ; S = sc . nextLine ( ) ; char [ ] c = S . toCharArray ( ) ; Arrays . sort ( c ) ; String ans = " " ; for ( int i = 0 ; i < N ; i ++ ) { for ( int j = 0 ; j < N ; j ++ ) { if ( c [ j ] == ' \0' ) continue ; if ( count ( ans , c , c [ j ] ) > K ) continue ; ans += c [ j ] ; c [ j ] = ' \0' ; break ; } } System . out . println ( ans ) ; }
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