public static void main ( String [ ] args ) throws IOException {
  BufferedReader br = new BufferedReader ( new InputStreamReader ( System . in ) ) ;
  String [ ] setting = br . readLine ( ) . split ( " " ) ;
  int nameNum = Integer . parseInt ( setting [ 0 ] ) ;
  int kitLetterNum = Integer . parseInt ( setting [ 1 ] ) ;
  String [ ] nameArray = br . readLine ( ) . split ( "" ) ;
  String [ ] kitArray = br . readLine ( ) . split ( "" ) ;
  int count = 1 ;
  int nullNum = 0 ;
  while ( true ) {
    for ( int i = 0 ;
    i < kitLetterNum ;
    i ++ ) {
      for ( int j = 0 ;
      j < nameNum ;
      j ++ ) {
        if ( nameArray [ j ] == null ) {
        }
        else if ( nameArray [ j ] . equals ( kitArray [ i ] ) ) {
          nameArray [ j ] = null ;
          nullNum ++ ;
          break ;
        }
      }
    }
    if ( nullNum == nameNum ) {
      break ;
    }
    else if ( count == 50000 ) {
      count = - 1 ;
      break ;
    }
    else {
      count ++ ;
    }
  }
  System . out . println ( count ) ;
}

public static void main ( String [ ] args ) throws IOException { BufferedReader br = new BufferedReader ( new InputStreamReader ( System . in ) ) ; String [ ] setting = br . readLine ( ) . split ( " ▁ " ) ; int nameNum = Integer . parseInt ( setting [ 0 ] ) ; int kitLetterNum = Integer . parseInt ( setting [ 1 ] ) ; String [ ] nameArray = br . readLine ( ) . split ( " " ) ; String [ ] kitArray = br . readLine ( ) . split ( " " ) ; int count = 1 ; int nullNum = 0 ; while ( true ) { for ( int i = 0 ; i < kitLetterNum ; i ++ ) { for ( int j = 0 ; j < nameNum ; j ++ ) { if ( nameArray [ j ] == null ) { } else if ( nameArray [ j ] . equals ( kitArray [ i ] ) ) { nameArray [ j ] = null ; nullNum ++ ; break ; } } } if ( nullNum == nameNum ) { break ; } else if ( count == 50000 ) { count = - 1 ; break ; } else { count ++ ; } } System . out . println ( count ) ; }
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