public static void main ( String [ ] args ) {
  Scanner sc = new Scanner ( System . in ) ;
  int n = sc . nextInt ( ) ;
  int [ ] [ ] chars = new int [ n ] [ 26 ] ;
  for ( int i = 0 ;
  i < n ;
  i ++ ) {
    String s = sc . next ( ) ;
    for ( int j = 0 ;
    j < s . length ( ) ;
    j ++ ) {
      chars [ i ] [ ( int ) ( s . charAt ( j ) - 'a' ) ] ++ ;
    }
  }
  String ans = "" ;
  for ( int i = 0 ;
  i < 26 ;
  i ++ ) {
    int min = Integer . MAX_VALUE ;
    for ( int j = 0 ;
    j < n ;
    j ++ ) {
      min = Math . min ( min , chars [ j ] [ i ] ) ;
    }
    for ( int j = 0 ;
    j < min ;
    j ++ ) {
      ans += ( char ) ( i + 'a' ) ;
    }
  }
  System . out . println ( ans ) ;
  return ;
}

public static void main ( String [ ] args ) { Scanner sc = new Scanner ( System . in ) ; int n = sc . nextInt ( ) ; int [ ] [ ] chars = new int [ n ] [ 26 ] ; for ( int i = 0 ; i < n ; i ++ ) { String s = sc . next ( ) ; for ( int j = 0 ; j < s . length ( ) ; j ++ ) { chars [ i ] [ ( int ) ( s . charAt ( j ) - ' a ' ) ] ++ ; } } String ans = " " ; for ( int i = 0 ; i < 26 ; i ++ ) { int min = Integer . MAX_VALUE ; for ( int j = 0 ; j < n ; j ++ ) { min = Math . min ( min , chars [ j ] [ i ] ) ; } for ( int j = 0 ; j < min ; j ++ ) { ans += ( char ) ( i + ' a ' ) ; } } System . out . println ( ans ) ; return ; }
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