import java.io.*;

class CharListAIO
{

 public static void print(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 read(BufferedReader in) 
 throws IOException,ListFormatException
 {
  String excmess,line = in.readLine();
  CharListA L=null;
  try {
       if(line.charAt(0)!='[')
          {
           excmess="Expected '[', found '"+line.charAt(0)+"'";
           throw new ListFormatException(excmess);
          }
       else if(line.charAt(1)!=']')
          L = new CharListA(line.charAt(1),readRestList(line,2));
      }
  catch(StringIndexOutOfBoundsException e)
      {
       excmess="Unexpected end of line";
       throw new ListFormatException(excmess);
      }
  return L; 
 }

 private static CharListA readRestList(String line,int i)
 throws ListFormatException
 {
  String excmess;
  if(line.charAt(i)==']')
     {
      if(++i!=line.length())
         {
          excmess="Extra characters: \"";
          excmess+=line.substring(i,line.length())+"\"";
          throw new ListFormatException(excmess);
         }
      return null;
     }
  else if(line.charAt(i)!=',')
     {
      excmess="Expected ']' or ','";
      excmess+=", found '"+line.charAt(i)+"'";
      throw new ListFormatException(excmess);
     }
  else
     return new CharListA(line.charAt(i+1),readRestList(line,i+2));
 }
}