""" 
The script markov.py reads text from standard input and 
writes
a pagragraph of text to standard output.  Blank lines in 
the 
input are treated as paragraph separtors and are 
represented
as '\n' in the code.
"""
import random

nlnl = '\n', '\n'

def new_key(key, word):
   if word == '\n': return nlnl
   else: return (key[1], word)

def markov_data_from_words(words):
   data = {}
   key = nlnl
   for word in words:
       data.setdefault(key, []).append(word)
       key = new_key(key, word)
   return data

def words_from_markov_data(data):
   key = nlnl
   while 1:
       word = random.choice(data.get(key, nlnl))
       key = new_key(key, word)
       yield word

def words_from_file(f):
   for line in f:
       words = line.split()
       if len(words):
           for word in words:
               yield word
       else:
           yield '\n'
   yield '\n'

def paragraph_from_words(words):
   result = []
   for word in words:
       if word == '\n': break
       result.append(word)
   return ' '.join(result)

if __name__ == '__main__':
   import sys
   print paragraph_from_words(
           words_from_markov_data(
               markov_data_from_words(
                   words_from_file(
                       sys.stdin))))