public static void main ( String [ ] args ) {
  Scanner s = new Scanner ( System . in ) ;
  int times = Integer . valueOf ( s . nextLine ( ) ) ;
  ArrayList < String > list = new ArrayList < String > ( ) ;
  String word = s . nextLine ( ) ;
  for ( int x = 0 ;
  x < word . length ( ) ;
  x ++ ) {
    list . add ( "" + word . charAt ( x ) ) ;
  }
  for ( int x = 1 ;
  x < times ;
  x ++ ) {
    ArrayList < String > temp = new ArrayList < String > ( ) ;
    word = s . nextLine ( ) ;
    for ( int y = 0 ;
    y < word . length ( ) ;
    y ++ ) {
      String a = "" + word . charAt ( y ) ;
      if ( list . contains ( a ) ) {
        list . remove ( list . indexOf ( a ) ) ;
        temp . add ( a ) ;
      }
    }
    list = temp ;
  }
  Collections . sort ( list ) ;
  String build = "" ;
  for ( String thing : list ) build += thing ;
  System . out . println ( build ) ;
}

public static void main ( String [ ] args ) { Scanner s = new Scanner ( System . in ) ; int times = Integer . valueOf ( s . nextLine ( ) ) ; ArrayList < String > list = new ArrayList < String > ( ) ; String word = s . nextLine ( ) ; for ( int x = 0 ; x < word . length ( ) ; x ++ ) { list . add ( " " + word . charAt ( x ) ) ; } for ( int x = 1 ; x < times ; x ++ ) { ArrayList < String > temp = new ArrayList < String > ( ) ; word = s . nextLine ( ) ; for ( int y = 0 ; y < word . length ( ) ; y ++ ) { String a = " " + word . charAt ( y ) ; if ( list . contains ( a ) ) { list . remove ( list . indexOf ( a ) ) ; temp . add ( a ) ; } } list = temp ; } Collections . sort ( list ) ; String build = " " ; for ( String thing : list ) build += thing ; System . out . println ( build ) ; }
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