import java.io.*;

class UseCharListsA3
{
// A program which reads and writes lists of characters
// in their conventional form.
// Has recursive list reading and writing methods

 public static void main(String[] args) throws IOException
 {
  BufferedReader in = new BufferedReader(
                        new InputStreamReader(System.in));
  CharListA L1,L2;
  System.out.print("Enter first list of characters: ");
  L1 = readCharListA(in);
  System.out.print("Enter second list of characters: ");
  L2 = readCharListA(in);
  System.out.print("The lists are: ");
  printCharListA(L1);
  System.out.print(" and ");
  printCharListA(L2);
  System.out.println();
 }

 public static void printCharListA(CharListA L)
 {
  System.out.print("[");
  if(L!=null)
     {
      System.out.print(L.head);
      printRestList(L.tail);
     }
  System.out.print("]");
 }

 private static void printRestList(CharListA L)
 {
  if(L!=null)
     {
      System.out.print(","+L.head);
      printRestList(L.tail);
     }
 }

 public static CharListA readCharListA(BufferedReader in) 
 throws IOException
 {
  String line = in.readLine();
  CharListA L=null;
  try {
       if(line.charAt(0)!='[')
          {
           System.out.print("Error - expected '[',");
           System.out.println(" found '"+line.charAt(0)+"'");
          }
       else if(line.charAt(1)!=']')
          L = new CharListA(line.charAt(1),readRestList(line,2));
      }
  catch(StringIndexOutOfBoundsException e)
      {
       System.out.print("Error - unexpected ");
       System.out.println("end of line");
      }
  return L; 
 }

 private static CharListA readRestList(String line,int i)
 {
  if(line.charAt(i)==']')
     {
      if(++i!=line.length())
         {
          System.out.print("Error - extra characters: \"");
          System.out.println(line.substring(i,line.length())+"\"");
         }
      return null;
     }
  else if(line.charAt(i)!=',')
     {
      System.out.print("Error - expected ']' or ','");
      System.out.println(", found '"+line.charAt(i)+"'");
      return null;
     }
  else
     return new CharListA(line.charAt(i+1),readRestList(line,i+2));
 }
}