#!/usr/bin/env python

import sys
import re
import string

MAX_LINE_LENGTH = 1024
MAX_WORD_LENGTH = 50

LINE_DELIMITERS = set('.,;:!?')
RE_HAS_LINE_DELIM = re.compile('[\.,;:!?]')

RE_NON_ACCEPTIBLE_CHARS = re.compile('[^A-Za-z0-9\']')
RE_REMOVABLE_QUOTES = re.compile('([^A-Za-z])\'([^A-Za-z])')
RE_WHITESPACE = re.compile('\s+')

def process_line(line):
    if not isinstance(line, str):
        line = ' '.join(line)

    if len(line) > MAX_WORD_LENGTH: return

    line = RE_NON_ACCEPTIBLE_CHARS.sub(' ', line)
    line = RE_REMOVABLE_QUOTES.sub(r'\1 \2', line)
    line = line.lower()
    line = RE_WHITESPACE.sub(' ', line)
    line = line.strip()

    words = line.split(' ')
    for w in words:
        if len(w) > MAX_WORD_LENGTH: return

    # get 1,2,3 grams
    for i in xrange(len(words)):
        uni_gram = words[i:i+1]
        bi_gram = words[i:i+2]
        tri_gram = words[i:i+3]

        if len(uni_gram) == 1: print ' '.join(uni_gram)
        if len(bi_gram) == 2: print ' '.join(bi_gram)
        if len(tri_gram) == 3: print ' '.join(tri_gram)

def main():
    line = []

    for l in sys.stdin:
        line_sum = sum([len(x) for x in line])
        if line_sum > MAX_LINE_LENGTH: line = []
    
        lines = RE_HAS_LINE_DELIM.split(l)

        if len(lines) == 1:
            line.append(lines[0])
        else:
            line_segment = lines.pop(0)
            line.append(line_segment)

            process_line(line)

            line = [lines.pop(-1)]

            for l in lines:
                process_line(l)

if __name__ == '__main__':
    main()